I am very experienced with laser and I still get anxious when I go in. It hurts, but it's worth it!
So what happens is your hairs are zapped and fried the day you have laser, however it takes the body some time to push those fried hairs out. One reason for this is that shaving so closely prior to laser means there is nothing to grab onto those dead follicles for a while to pull them out. Eventually daily activities, sleeping, shaving etc will get them all. They lasered hair only APPEARS to grow...really they just get pushed out (and you can even push them back in....its just a little tube of hair in a hole at that point there is no bulb at the end as that is toast).
To speed my reults I usually let my hair grown out a few mm, then I epilate by taking a little duck strip and putting it over my face. I pat it then lightly pull and only the dead hairs come out while the unaffected hair stays put. It doesn't hurt one bit...and I love seeing all the fried hair come out with ease and stuck to the tape!
You will eventually learn to distinguish the hairs that were cooked from the ones that made it through the process, and thus which ones are growing vs. just being pushed out. The tell-tale sign for me is that a hair will fall out if it has a tiny scabby sort of skin around it...AND basically the hair just looks funky, cooked, and sad. Those are the winners!
I had a really dense, dark beard and I'd say I agree that 18 months is what it will take, though now my appointments are 6 weeks apart. In the days following a session your beard may appear worse, and that is due to the heat-wilted tip of the hair which is more prominent than the usually nicely cut blunt end of the hair.
Laser is absolutely worth it. I just look on groupons and double take deals for coupons like "6 laser sessions for $150." I have had about 97% of my previously dark horrible beard removed for probably less than $1000 including numbing cream. Check for deals and stick with it.
Oh yes...keep your face very clean immediately after laser (NO MAKEUP!) otherwise you risk some super painful pimples.