I live in a hot climate region.I have some potted plants that i rooted in march and they are being potted in compost.What would be an appropriate time to transplant them in the ground?
In Greece the temperature easily reaches 35 celsius in summer.
Would i have to wait till september when temperatures fall naturally? Do i have to wait till the plants get dorman and drop their lives and then transplating them to the ground?

Shade cloth works wonders

If you water daily and don't disturb the rootball, it's ok. Drip irrigation is best.
If drip irrigation is not available, water early or late afternoon. I would do as Tony says.

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What has worked for me was to water in with seaweed concentrate to alleviate any transplant shock. After that i placed them in shade for about a week and slowly ease it into a full sun position. Works every time and i never lost a fig tree this way. even one that had lost 80% of its root mass due to damage in postage. I did lose one when i put it in full sun with no seaweed concentrate after transplanting. 

I plant all year around except sever cold during winter.  But when I plant I use Fertilome's Root Stimulator.  It reduces the plant shock.  It's a liquid that mixes with water.  For container trees, I soak the root ball in the mixture for an hour first, then plant it.  If I'm planting in the ground, I dig my hole, pour in the mix, add the tree, rack around the soil and add more mix.  I haven't lost a tree yet using that method.

Hi,
A potted tree can be planted anytime you want.
What you can't do is move an in ground tree during the heat, because you'll severe the roots, and that will be a problem.
A potted tree, you don't touch the roots, so it is safe to plant them even in summer.
It is up to you to transition the cutting to full sun before and then plant them in the ground.
I've done it several times and they get even happier, because they have more nutrients and less direct heat at the roots.
Of course, you've been watering your cuttings, and will have to keep on doing so.
Other gardeners and myself use to water regularly a young planted tree the first two years at least..
Good luck !