Hi ghoot,
I'm just a beginner with PBP (lots of fun! :-), so keep that in mind ....

Noticed that the B4-7 interrupt is left enabled during the "lowpower" section. Could a B4-7 pin state change be causing the early wakeup?

Might also try using the "disable" instruction before the "lowpower" section instead of turning your interrupt enable bits on and off. Then just clear the flag[s] as needed before re-enabling interrupts.

Something like this...
ON INTERRUPT GoTo myint
;
;Some code here
;
Disable ; Turn PBP interrupt checking Off.
lowpower:
Sleep TimeDely
INTF=0 ; Clear the RB0/INT interrupt flag (what about the B4-7 flag??).
Enable ; Turn PBP Interrupt checking back on.
Sleep 7200 - TimeDely
'DO SOME OTHER STUFF HERE
GoTo lowpower


Should save a bit of code space, as PBP will not insert the statements that check to see if an interrupt occured (inserted before every command when "OnInterrupt" is enabled).

Archilochus