Squab's grow from day to day at an enormous rate.And every squab is differant.
Some you have to band at five day's, othere's seven. If you can put the band on a bird with a little resistance ( band to leg resistance).
You got it. If it keep's falling off. Wait until the next day.
If you think you cannot get the band on, get some petroleum jelly or good ole spit. It's very much like taking your wedding ring on or off.
Hope I helped.