SN6505B: External Clock Requirements

This wasn't clear to me in the SN6505 spec: Can I apply/remove an external clock at any time and have the SN6505 use it if applied (and fall back to internal if not)? I see the T_CLKTIMER interval, which suggests that if the external clock goes away, the SN6505 will pause for about 20 uS and then switch over to run from its internal clock. But if I later re-apply an external clock, will it switch to using the external clock again? Or is the evaluation made only once at power-on or enable asserted? Thanks