I did, but it wasn't before he was supposed to be in boxes. He told me he was leaving the 4th, I TT'd to the third, then to the 10th. And he's just gone.
I've done similar things in the past with no ill effect.
your game didn't bug. here is what happened
he told you that he was leaving the 4th, and said that his last day would be on the 10th
when you TT'd back to the 3rd, the leaving date changed to the 8th
basically the leaving date isn't set on stone, it's just x days from the day that he told you
in this case, it was six days.
so if you hadn't tt'd backwards, here is what would have happened:
4th - he'd tell you that he was leaving on the 10th
(day 1) 5th - he'd still be there
(day 2) 6th - he'd still be there
(day 3) 7th - he'd still be there
(day 4) 8th - he'd still be there
(day 5) 9th - he'd still be there
(day 6) 10th - he'd be in boxes
but since you tt'd backwards:
4th - he'd tell you that he was leaving on the 10th
(day 1) 3rd - he'd still be there, but the leaving date would have changed
(day 2) 4th - he'd still be there
(day 3) 5th - he'd still be there
(day 4) 6th - he'd still be there
(day 5) 7th - he'd still be there
(day 6) 8th - he'd be in boxes
(day 7) 9th - his house would be gone
(day 8) 10th - his house would be gone