It depends on what you mean by last. I tend to use the same group of guys, and we work together off-and-on over the years. So even though the 'band' might not last, the working relationships do. And sometimes the band may last too, even though they may not get together often. For example, I put together a Blues band together years ago for a pickup gig. We wound up doing a few gigs and then left it open ended after that. We don't get together to rehearse, and we only do pickup gigs, but we do about 1-3 shows a year over the last couple years. Which is fine, because everyone has other gigs to fill their time.
+1 to this ^^^
Same with my Celtic-cum-country-cum-pseudo jazz swing-cum-weddings/corporate events band. I'm not the one with the talent, but the other principal players are and I get to ride on their coattails. Extra players are added as necessary, tailored to the gig. The blues/swing band I'm in (the only one I've formed myself) is much the same. No rehearsals, unfortunately for me.
My other originals-band has rehearsals (thankfully), we'll do a mini-tour of China in the fall to support the band's 2nd (my first) CD, launching it locally in June/July.
A percussionist friend has a latin band of between 8-11 players depending on work schedules/other commitments. They practice regularly because they love the music and the hang. It took a long time to get it all together, a couple of years before it stabilised somewhat.
- Pickup bands are great for the cash, some fun and low commitment/rehearsal levels;
- Long-haul commitment bands are equally great for different reasons, for the love of the chosen style of music and some fun.
So many variables factor into the time to form a band.
Different types of bands, different types of situations.
My advice is hang out with other musicians, whether you're playing with them or not. Also, play in genres outside your comfort/preferred zone to meet yet more musicians. You don't spearfish in a desert, you've got to immerse yourself.
