Abe has been working on the small experimental box. Aaron balances the feed. Abe learns of its function for time travel. He builds a large box. He does not use it. He plans on building a second box. Unbeknownst to himself, the first box actually works, Aaron has exited the box. This is Aaron(2) who has been convinced by Aaron(3) to leave. He calls Abe and tells him about the time travel boxes. Now Abe uses the fail-safe box,.only it is after Aaron(3)and(2) already arrive.
First, we have to understand that Abe was capable of building the boxes, even if he thought it was for gravitational experiments. He made the first time travel box. It is possible that he turned it on and his future self exited. Actually, nothing happened according to what Abe says. He viewed it as a time machine and installed the timer to prevent ever meeting his future self (or his past self). Otherwise, he would get in the box at 3:00, and then a stunned Abe(1a) met the exiting Abe(1b). That makes Abe(1a) a temporary Abe, as long as he repeats himself from the former time line and gets back in the box at 3:00.
If Abe recognized that he built a time machine, he may have decided to keep it secret for a little while, learn control, make rules, then let Aaron know. But, since the time lines overlap, as illustrated above, then, as we see in the end, Abe builds the box and gets a call from Aaron(2). Now even if Abe(2) sabotages the box, Abe(1) will not stop until he experiences making and using the box.
Abe should recognize that, since he got a call from a future Aaron, that the cycle is repeating itself. But instead of calculating that there is another Aaron running amok and that he can not gain the upper hand, Abe assumes with the knowledge he gets from Aaron(2), that he will get and keep the upper hand over Aaron(1). And this could be true, unless Aaron(1) gets thrown into the attic and escapes to find the fail-safe. Or if Aaron(3) meets Abe, which puts Aaron(1) into the attic just as Aaron(2) had done the time before. Poor guy. In Abe's defense, it would be a lot to absorb. This is probably why Abe feels he can keep Aaron from causing such a disruption by slowly guiding and teaching him. (If it was only Aaron(1) but, of course, it isn't.)
Is this already a paradox? It may seems to be because of the overlapping of the time lines. It seems almost like Dr. Brown's line in Back to the Future, "Time machine? I haven't invented any time machine yet." And this is Abe, only there is a four day gap instead of thirty years. Since Abe is unable to comprehend that Aaron exits the first box turned on, he doesn't understand how the Argon is leaking out. Obviously, some leaks out when Aaron gets in at the B end and opens the door once again when he arrives at the A end.(plus any residual leaks over an eight day period. This is why Abe is concerned, "There's always leaks." Aaron is truly surprised by this, "There's leaks!". Since neither of them takes an Argon bottle to replenish, one must assume that there is enough Argon in the box at the B end to facilitate the full trip back to the A end. It should also be noted that the fungus is never brought up again.
