Getting the seed in the 75 to 85 degree range made the difference between 6 to 7 days and 3 weeks for me. Mine have ranged from 6 days to 25 days. The 25 day one is College 64L that came as a sample from Totally Tomatoes in 2007. I had one out of 6 germinate. On the other hand Chinese Giant from the same source is 11 of 14.
If they are below 75 or better 80 warm them up and wait a little longer.
I germinate mine at 80 degrees. Make sure they are not planted too deep. I cover mine with about 2-3 millimeters of soil. Also, make sure they are not old seeds. I am still sowing Big Dippers from 2007 and my germination rate is decreasing each year. I don't know if I will be able to sow any of them next year with any success but I am sure gonna try! However, they didn't do really well this year at all but I still got enough for my family to plant. Good luck with them.