I like to divide daylilies in the fall- at least 6 weeks before the first frost, sooner if they have finished flowering for the year. This gives them time to recover, grow new roots, and get ready to flower again sooner. If you wait until spring, they take longer to start flowering again.

I agree about the day lilies. as for the gerberas I don't grow them so I don't know the correct answer, but if you are going to split them before the winter then I would do it asap, to give the plants time to settle back and make new roots etc. If you do it in the spring then after frosts unless you can give the plants winter protection [frost free].

Thanks to both the guys quick responses above,as a novice gardener to be able to get advice from more experienced gardeners is great .....thanks again