It depends on the soil you are using. Fox Farms Ocean Forest will support plants without feeding for 3-4 weeks. As far as when to transplant it depends on the size of the pots you started with. I just transplanted 30 day old seedlings in 8 inch pots. These were 10-11 inches tall and quite bushy. Never feed them till transplanted as i started them in Fox Farms Ocean Forest. I transplant into Sunshine #4 and start feeding at 50% does right away as #4 doesnot contain fert.
You want enough root growth throughout the pots so the soil holds together when you transplant. I had no transplant shock at all with these seedlings.