I've also had this problem - going back to school and night classes are on the night I was going to my home group and it wrecked a 5 year "habit." I've gone weeks without a meeting, but I stay in touch with others in recovery, post on here, work with someone on their recovery and I continue to do my daily prayers etc while looking for another meeting to attend. Been to several that didn't "click" so I'm still looking. If you have a sponsor, just check in with them every once in a while, and monitor yourself. If you start getting particularly irritable, restless, depressed or angry, and especially if you start obsessing on drinking than that's a good time to find a meeting ASAP. Otherwise, there's no magic time frame that says if you miss "X" amount of meetings you're doomed. Meetings are one of the valuable tools we use to stay sober and to find ways to help others, but they aren't the only thing between us and a drink.