I grew half and half - six 80/20 Sativa and six 50/50 Indica/Sativa.
The Sativa flowered first; the hybrid lagged far behind until the very end when it took off.
The Sativa bud growth seemed more linear where the hybrid seemed more exponential given the same time-line; in both cases, towards the end of flowering, they got pretty fat. Unfortunately, mother nature stepped in and put the kybosh on my grow a couple of weeks early.
My hypothesis is that my Sativa (Maui Wowie), given the drastic difference in latitude between where it originates and where I was growing it (New England), probably prompted the early flowering, but that is just conjecture on my part.
Maybe someone with a greater understanding of the science behind this will comment.