Warmers aren't just about getting the tyres hot tho... if they're left on between sessions they'll serve two purposes.
First they'll help keep the tyres withing a certain heat range all day, preventing the rubber degredation through heat cycles - heat cycles make a lot of difference when the tyres are at TRACK temp rather than riding-to-work temp;
and secondly, they'll heat up the wheel rims, thus providing an additional heat supply to the tyre whilst waiting in the collecting area.
So it's a perfectly good choice to get them warmers.
Last year I was rolling round on 208GP's, which heat up just by turning the engine on! Probably not a good choice for lots of road miles tho, but that's a different thread!