Thanks for the contribution - it had me thinking for a while as to why it should improve performance.  We are always desperate for improvements in database query performance so every idea is very welcome.

The idea of this restriction is to not show events that started more than 24 hours ago if they are configured not to appear on second or subsequent days.  I'm interested that this should have much impact on the query speed - I wonder if you can tell me a little about the types of events you have on your site - e.g. mix of single and multi-day events?  etc.

Strictly speaking we should be testing for rpt.startrepeat before midnight as opposed to 24 hours before the startdate and also we should have an OR statement in there too to handle the multi-day events that should be appearing.  Adding the OR is likely to make the query a lot slower I suspect.