If you go back to October 2005, on LBC Iain Lee was moved from late nights weekends to 4-7 weekdays to replace Daisy Sampson, and then to 3-6.30 in January 2006. That was seen to be very bold at the time but Iain got far more listeners. (Iain used to regularly quote the RAJAR figures). It is seen by many Iain Lee fans as his finest work. Jon Holmes, and occasionally Nick Abbot, would sit in for him. However, despite the show's success, the pressure to put on a more sensible drivetime show was too great and Iain was moved to 7-10 pm in January 2007 which is always a bit of graveyard slot as it is the main TV watching time.
Nick Abbot used to do 7-10pm on Talk Radio in the late 90s and said in 2006 that Iain would do well in that slot. I thought Iain's show was still excellent in the evening, however callers were a bit thinner on the ground. Iain said that on drivetime, he and Agent Chris had a lot of choice of callers and it was quite hard to get on.
However, at the same time Jon Holmes was given Friday drivetime (Monday to Thursday was Paul Ross) and it was a comedy phone-in, although there was one Friday when he did serious topics, which was a mystery at the time. I think Jon could do pretty much any slot, and indeed he's pretty much done all slots from breakfast to drivetime. I haven't heard him in the evening though. Maybe he doesn't want to work in the evenings?
I wonder who will be sitting in for Jon and Iain when they go on holiday?