When is the best time to move Photina Red Robin trees?

Hi Gardenamateur, welcome to GOY.
It's almost time for you if you live in the north or Scotland.Here in the south it is still very warm and they would flag when moved with the warmth of the sun. Also we are still very dry and need more rain to make moving/growing conditions better. Wait a month or so if you live in this area.

Just a little question here, as you're calling them "trees", how big are they and how long have they been planted there? Because if they are genuinely tree sized, it will be virtually impossible to move them successfully without machinery to carry the rootballs.

A big thank you for your replies, I only moved into my property in Northamptonshire last December and haven't pruned them at all. They look like they might have been there for 3-4 years. They are now 6.5-7ft tall, the trunks are very narrow however (am not too sure how wide the trunks could grow...). Any further advice titbits welcome!!

Well you could have a go at moving them when the weather cools a bit, but it might not be very successful - if they're that large, you might find the roots impossible to extract without severe damage. You will have to chop down half the topgrowth for any remote chance of success, too, but I'd have a go if they're in the wrong place - if you can't get them out intact, you will have to just rip them out and buy new if you want to replant Photinia elsewhere. It's easy to get hold of, not that expensive.