when can I add nutes to my soil?

I have some plants in a soil that I picked up at lcl lawn and garden shop.
After reading this site for a while I have come to the conclusion this may be a problem.
I want my plants to have enough nutes.
This soil said on the bag that it was a time release for up to 9 mo's.
The plants are only 3 weeks old. They seem to be doing good for now.
I am just wondering about the later parts of the grow.
I am thinkin I should get some better soil to transplant these into next time I increase pot size.

all comments welcome

You picked up pot plants at a lawn and garden center?

lol is that what i said
I meant I got the soil there
HeHeHe

dam i was about to say ima check that out .. that's odd

mate leave the nutes for aleast 4 weeks in good soil b4 adding nutes