Is there a best time to leave the UK for a year abroad?

I have a client who is planning on working in Canada for a year, starting next year. 

They plan to leave in either March or June, and wondered if it is better to leave before or after the end of the 11/12 tax year, or whether there is no benefit either way. 

I am not a tax expert so don't feel I can advise in detail on this matter, so any advice would be gratefully received