Blinky, the timeline depends on how you handled germination. If you stick them straight into rockwool it very well could take more than 3 days.
I soak mine for 12-24 hours, then put them in a wet paper towel. The taproot can take 1-3 days to pop out. From there plant them in rockwool/soil whatever, you should see them 2ish days later. Total time to see them for me = 4ish days on avg. So, if you just put the seeds in rockwool, it might take a while, maybe 5 days+.