"Just so you know," said Theo as he rummaged in his pockets, "it really was an accident, what happened that day with my Alchemical experiment."
"I believe you," said Oleandra softly, as Theo placed the Time-Turner in her palm. "Now, tell me everything you know."
As long as its occupant didn't wish to be found, the Room of Requirement would remain sealed to all others, so they had all the time in the world… as long as it didn't exceed five hours.
"Well, it happened like this," Theo began. "I was in the wrong place at the wrong time, you see."
Theo then went on to explain what had happened, to the best of his knowledge.
After being barred from the Alchemy classroom and banned from Professor Dumbledore's lessons for what he'd done to Oleandra, he had started secretly using the Room of Requirement to conduct his experiments in his free time.
Tonight was no different. But some time into his experiments, the room had suddenly started shifting on its own. The archway had appeared in the middle of the room, making a mess of his Alchemical array, and it had emitted a bright flash of light. And just like that, Theo had found himself surrounded by Dwarves and Death Eaters.
"If my father hadn't been a Death Eater, I probably wouldn't be talking to you right now," Theo admitted. "In any case, your sister came in through the door about five minutes later. From there, she and Malfoy split up their forces and began preparing their ambush. Apparently, Professor Dumbledore was meant to return to the castle by broomstick, so they rushed to the roof, while the rest went down to the stairs to barricade the way up."
Oleandra checked her pocket watch. It was ten past midnight.
"Right, then," Oleandra muttered to herself. "The Time Turner's limit is five hours, so that's what we'll use, just to be safe."
"About that…" Theo said hesitantly. "After dinner at eight o'clock, I did my homework until a little past three in the morning, then used the Time-Turner to go back to ten o'clock to do my experiments."
In other words, Theo had already used all five of the Time-Turner's allotted hours. The future from ten o'clock to three in the morning was already set in stone, even though Oleandra hadn't experienced it yet.
"Three o'clock and how many minutes?" Oleandra asked in desperation. "How many minutes, Theo!?"
At any given moment, there could be up to n+1 copies of the same person: the original, and n time-duplicates. This could be achieved by going back one hour, waiting for that hour to pass, and then repeating this process as many times in a row as one wished.
Though it was risky, it wasn't against the rules to have more than one time-duplicate running around at once— so long as one didn't travel more than five hours back from the point of initial activation. So, it wouldn't be a problem for Theo to make another trip, as long as he didn't go further back than ten o'clock.
"I didn't think to check," said Theo, scratching his head. "How was I supposed to know all of this was going to happen? I wasn't planning on going back in time a third time to get more sleep. Ageing twice as fast is bad enough already."
Oleandra checked her pocket watch once again. Twelve past midnight. Since Theo wasn't certain when he'd turned back time the first time, it was too risky to wind the Time Turner twice. For instance, if he'd returned to the past at 10:20 and Oleandra wound the Time-Turner twice right now, she'd arrive before Theo had at 10:12, breaking the five-hour rule by eight minutes.
"One twist is the limit," said Oleandra grimly. "One hour."
After having spent a few months in the distant past, she wasn't risking meddling with time.
"Or, we could wait another twenty minutes," Theo suggested, "that way, we'd ensure we didn't overshoot the time limit, and we'd have two hours."
In the silence that followed, Oleandra realised the sounds of fighting outside had already stopped. In all likelihood, Snape had already fled up the stairs and flown away.
"Open up! We know you're still out there!" a reedy voice called through the door, punctuated by loud banging. "You're only making things harder for yourself! I'll have you know Rowena Ravenclaw herself built this room, and as Head of Ravenclaw, I can assure you I'll have this door open in no time!"
Oleandra and Theo shared a nervous look. Forget five hours— they didn't even have a minute! So long as there were enough people on the outside, their need to enter would outweigh the need of those inside for a place where they couldn't be disturbed, and the Room of Requirement's door would swing open.
"Behind the door!" said Theo urgently, pointing at the exit. "If I'm about to enter the Room of Requirement, or if I'm already inside one hour in the past, I won't think to look behind it!"
"Is there any chance that Malfoy and Daphne might already be in here?" asked Oleandra.
"They might be," Theo admitted. "I didn't get much work done before the Archway appeared."
The voices outside were growing louder. The castle was now fully awake, and the Aurors had no doubt already arrived from the ministry, so Oleandra and Theo hurried to the door and slipped the Time-Turner's chain around their necks.
"Ah, just a second," said Oleandra, withdrawing a tube of lipstick from her pouch, tracing the reversed rune of secrecy on her cheek and Theo's in red. "Perthro!"
She realised now that the voice she'd overheard through the Peruvian Instant Darkness Powder couldn't have been Daphne's— meaning it must have been her own. But since everyone had been surprised to see her earlier, she couldn't show herself to the others wearing her own face.
Oleandra's and Theo's forms shimmered, growing blurry before resolidifying into Daphne's and Professor Flitwick's. If the Charms teacher had only just now arrived, then it stood to reason they wouldn't run into him in the past.
"Hurry up!" hissed Theo.
Oleandra carefully twisted the Time-Turner's golden hourglass once, then let go. It began to spin rapidly in the opposite direction, and the world around them blurred into a whirl of colour.