Ok, I've crunched some numbers and here's how Tidelocking works, and the practical upshot of it.
Tidelocking depends on several factors all at once: the mass of the star, the size of the planet, the age of the system, the initial rotation period of the planet, the tidal dissipation factor (Q) of the planet, and the orbital distance of the planet. Thus it's a bit hard to predict when it occurs, so we have to set a few things constant to get something predictable out of it.
e.g. We want to see if an earthlike planet is tidelocked around an M V star. So I put in a planet exactly like the Earth (initial rotation 10 hours, Q=20) in the habitable zone of stars with a variety of (low) masses and checked to see how old the system had to be before they got tidelocked. And here's what I got (hab zone distances are for initial stellar luminosities):
Mass Hab Zone Age to tidelock
0.1-0.6 within 0.29 AU within 0.1 Ga
0.7 0.39 AU 0.27 Ga
0.8 0.52 AU 1.20 Ga
0.9 0.67 AU 4.16 Ga (100 hrs at 3.75 Ga)
1.0 0.86 AU longer than age of star
0.6 solar masses (Ms) is K6 V, so anything in the habitable zone around stars between K6 V and M9 V will be tidelocked - no ifs, no buts.
0.7 Ms is K4 V.
0.8 Ms is K2 V.
0.9 Ms is G9 V.
So in practical terms, anything redder than about K2 V that is old enough to potentially allow life more complex than bacteria to form is going to have tidelocked planets in its habitable zone.
Smaller planets take longer to tidelock, but then as you get smaller you get less able to hold onto breathable atmosphere - however, a size 5 world (which can hold onto water, N2 and O2) basically tidelocks in about the same time as shown above - it seems you have to get a lot smaller before you can escape being tidelocked in that time.
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