I currently have my 4 week old plants on 18/6, last week they came on at 3pm and off at 9am. what with the clock chancge and shorter days would it be ok for me to move it forward an bit i.e off at 10am and on at 4pm?

Cheers

why????? but if you have to then yeah it should be ok

I muck about with vegging times a lot - usually go 24/7 when I'm home.

Doesn't seem to make any difference.

I don't think that your plants will mind you doing this one bit, IMHO - especially seeing as how they're vegging.