They germinate pretty fast, my buddy had seeds sprout the day after planting them. I would recomend against buying cactus seeds from an entheogen dealer/vendor, look for a breeder.
My buddy has 2 different sources for his seeds. He orderd 100(which was really 250) seeds from cactus plaza, and received around 30 for free from a friend. The 30 he received were very fresh, harvested the end of last year. The fresh ones started sprouting the next day after planting with 100% germination rate. The seeds he received from cactusplaza.nl took longer(5-10 days) to sprout and had about a 80% germ rate. Old seeds will take longer to break dormancy!
He has good results placing several seeds inside a ziplock bag and misting them lightly(for humidity, no pools of water). He then places the bag on a heat pad and 1 foot/12inch/30cm under a 23 watt Daylight spectrum CFL. You should see the seeds hatch and a little white ball with hairs(shaped like a microscopic octopuss). When the seedlings turn green put them in clay pots with a humidity dome. He does all his germinating, grafting, crowning, and rooting cuttings indoors. He then brings them out under a blue tarp when they are no longer vulnerable to the elements.
You wont be investing much time, just grow them as you live your life! They are pretty hard to kill, unless you get crazy with the nutes and watering can.