fan leaves turning yellow is usually not a good thing but that late in the flowering phase it is not the worst thing that could be happening just pay attention to the buds themselves.

A common practice is to trim 95% of fan leaves off 1.5 weeks before harvesting so that all the energy from the light is absorbed by the buds rather than the leaves. Keep in mind however that you need the fan leaves for proper plant production so don't get too chop happy. Actually, since is this your first grow maybe you should just skip that for this time until you feel more comfortable. But for now you should be watching the trichomes for sure.

Like hudson88 said depending on the high you want from the trichomes be your own judge!