I use a restorative composite to cement porcelain veneers because of its long setting time but I would like to know if I should be doing something differently?

Restorative composites are strong and have good physical properties. However, they are not usually used to lute ceramic restorations because their viscosity is too high. Also, there are no accessories in the kits for all-ceramic cementation, such as silane. I would recommend purchasing a resin cement kit that is specifically for luting. If you are primarily luting thin veneers, you could use a veneer cement that is light-cured only, so curing time is not an issue. Esthetic cement kits for cementing all types of ceramic restorations come with a catalyst and base so that you can cement thin restorations with light-cure only, and thicker ones using the chemically-cured catalyst. Most of these kits come with a silane, bonding agent, try-in pastes, and other accessories specifically for luting ceramic restorations.