José has already posted a reminder on the Announcements section but for any new hosts I thought I'd post a tip here to save you having to endure a roasting from your league members because race time shifted and it caught them unawares.
In the UK (and many other countries) clocks go forward 1 hour in the early hours of Sunday morning. Race times in iGP are aligned to GMT and do not change so if you want your races to continue to run at the same time you will need to edit the race time in the league settings. It is important to note that changes to race time do not come into effect for 24 hours, so if your league races on a Saturday you need to make the changes BEFORE the Saturday race takes place.
If you don't do this the Sunday race will run an hour later than usual.
I hope this makes sense.