SE IR
I think I remember reading in the IFR test prep notes from the CAA that minimum cloudbase for the test to go ahead in a single is actually 1000ft (for enroute) - this seemed sensible to me so I adopted it for any SE IR that I do ...
Remember 1000ft in most singles is less then a minute and a half with no engine - that assumes a straight in approach - if you ahve to turn its even less !!
500ft ... that has been suggested is about 30-40 secs once clear of cloud
Neil