Varies from person to person obviously, but aside from that, there's a difference in how quickly tolerance develops to specific benzodiazepine action. Hypnotic/sedative tolerance seems to set in the quickest, followed by muscle relaxant and anticonvulsant. Tolerance to anxiolytic effects develops rather slowly (and some people report being able to maintain a dose for 6 months or longer, but this is quite rare). Tolerance to amnesic effects develops very slowly as well.
Basically, with daily dosing of 10mg of diazepam - or equivalent doses of other benzos - I found that after 3 weeks, give or take, I had to double the dose for equivalent anxiolytic relief, and by the 2 month mark I was at 3x the original dose. Never went much higher; doctors didn't recommend it and I took their word for it. Have been on max 3mg alprazolam (which is short acting, to be fair) and 3mg clonazepam, so that comes out to 60mg diazepam, but I'd been on them for a while longer than I should have.
If you use benzos to get to sleep every night you may find you have to double your dose within a week - I've certainly had to when I've tried it. For anxiolytic effects the development seems to be at least twice as slow. For me.