I just put in some new trees last year, they've got a fence that's overgrown with honey suckles that blocking the morning sun at about a 55 degree angle, so it takes awhile for the sun to hit them. They're peach, nectarine, and orange tree, and I'm in California.

Hope this website gives you your answer---> http://www.gardenguides.com/68951-grow- ... arine.html

Is it just the morning sun that is blocked? If so, you are probably okay....I have seen a lot of trees in a lot of back yards and it seems to me that a bigger problem to worry about is a fruit tree that is surrounded more by a forest of tall trees around it than just by one fence blocking the morning sun.

You'd need to google the answer on that one but I suspect 6 hours is sufficient. Nevertheless, a cautionary tale is told on this website:

http://www.ehow.com/way_5745621_many-do ... need_.html

They will soon grow tall enough that they will be above the shade from a fence.