By "Seriousy affect" do you mean negatively? The idea is to achieve a positive response but there are things that can go wrong. How much of what potency fertilizer have you added to each bucket's growing media?

You should see a long term benefit (over 60 days) from a slow release fertilizer and the greatest benefit that I see is the root zone proximity of slower mobility nutrients. However slow release fertilizers typically sport a high nitrogen level and the coating (slow release property) is affected by moisture and temperature (variable). For that reason you don't want to use excess.

The fertilizer is called osmicote, the instructions say 3 tablespoons for 2' x 2' I put in a little more than 2 tablespoons for about 10l of regular potting soil

You didn't overfertilize. Osmocote releases so slowly that it can't burn your plants anyway. Hopefully you mixed it into the soil so the roots will find it later, I'm sure you did. Curling lower leaves is common and nothing to worry about but look at the undersides just to make sure it's not caused by aphids. Best of luck.