Hello fellow gardeners

I just today bought Helderfinger and Morello cherry trees.
The Helderfinger is a self pollinator and the Morello is partly self
fertile.
I assume that this pair will be ok planted 20feet apart?

But when?
What do they need?
What DON'T they need?

I have trawled the web and have not the answers, hence my Q

I live in UK just south of the Humber Bridge.....Sunny Scunny.

Any advice tips etc. will be welcome.

Thanks
Part_No