Diet is 95% of weight loss. During 5 months of the last year I went from 230 lb to 165 lb, so I can definitely confirm this. This weight change didn't affect my blood pressure at all - but I didn't have high blood pressure in the first place, it was normal even with 230 lb.
I personally don't see a point of going to ride (or to gym) for less than an hour - it'll be just an exercise in change of clothes.