For zapping rewards purposes, contiguous zaps are grouped into islands and treated as independent zaps. If that doesn't make sense, if you zap more later after other people have zapped, neither the early zap or the late zap influences the other - they are scored independently. It basically works in a game theoretically ideal way.

For post/comment ranking/rewards, zap order is irrelevant. Zapping X sats early in the order is the same zapping X sats late in the order. Zapping X sats early in the order, then Y sats later in the order, affects ranking the same as if you zapped X+Y sats all at once early or later in the order.