The normal start for evening matches during the season is 6.00 pm but this is obviously impractical in late season.
When clubs are agreeing evening T20 refixtures they should acknowledge this and agree a start time. As a minimum the late season dates when afternoon matches start times change should be followed i.e. from 8/08/15 to 21/08/15 start time 5.30 pm from 22/08/15 start time 5.00 pm.
Clubs may of course agree an earlier time should they wish and in very late season it may be advisable. If so, website and umpires should be informed.