The dream sequences are there just to remind you that you have "important mission" to do. No time limit in Fallout 2, if you exclude the 13 year hard coded limit.
SPOILER!
Spoiler
The condition of Arroyo is always the same when you return, and is not depending on how long you use to get to that point in main quest nor how many of those sequences you get.
End of Spoiler
"As we all know, holy men were born during Christmas...
Like mr. Holopainen over there!" - Marco Hietala, the bass player of Nightwish