They won't need anything other than the jiffy pellets at the initial stage and until after they sprout - and probably even through first set of leaves.
Then either transplant out of the peat pellets or with the peat pellets into a soil or other media. If you use potting soil versus something like coir that is without nutrients, the soil should be enough for a while. Be careful of "hot" potting soil/mix when the seedling are still quite young as they're sensitive to fertilizer concentration. Once they've had several days to root in you can start with a diluted/gentle application of something like fish fertilizer (the NPK's will seem wrong, but it works great) or a relatively balanced or tomato fertilizer (7-9-5 or 12-10-5 for example). There isn't any big hurry, though. If they're in coir or other media without nutrients, you'll need to start that diluted/gentle application reasonably soon after transplant as they won't have anything in the mix and you'll need to be more mindful of balanced ratios.
A big question is what you're transplanting them to, i.e., soil with nutrients or something like coir or perhaps even hydro, without. Also, there isn't any need to changed from a balanced NPK from beginning to end.