"What is taking so long?" Bill Cipher asked in irritation.

The whole point was to trick Sixer into opening the Weirdness Barrier for him.

Instead of torturing him, Bill Cipher left him to discover why the problem existed.

The Time Baby modified the Weirdness Barrier, the solution might not even work until it was fully studied.

"Gravity Falls, how amazing was it that the Time Baby stranded us here?" The Future Bill Cipher asked himself knowingly.

"He was expecting us, the Mystery Shack was already history before we got here." The Past Bill Cipher realized instantly.

"Complete Time Loop, only now the Time Baby is gone and somebody else is taking his place." The Future Bill Cipher explained.

"Who took his place?" The Past Bill Cipher asked worriedly.

"Another Bill Cipher at war with Cthulhu, the Humans lost and the Time Baby got resurrected again." The Future Bill Cipher explained.

"So the Time Baby returns and we get stranded here because of it?" The Past Bill Cipher asked worriedly.

"It gets worse, the Daleks are invading us!" The Future Bill Cipher declared back.

"Cthulhu versus the Daleks? Maybe Gravity Falls is safer than the rest of the world outside right now." The Past Bill Cipher realized instantly.

"No way, we're still Escaping Gravity Falls before the Time Baby returns!" The Future Bill Cipher declared back.