I agree with @scottc11. Using a timer is a simple solution that should work fine.
In general, if you have a slow input to measure, you count the time between edges with the system clock. If you have a really fast input, you count edges over a fixed time interval. The hardware timers in the Daisy processor are more than capable of both operating modes, running at the system clock rate.
Then it is just a math exercise to average or interpolate the period/frequency, divide it, multiply it, phase shift it, or whatever, to compute your internal event or sequencer clock period. You can use the next incoming edge to reset or resynchronize your internal clock to the input.
I had a lot of experience with PLL’s in my previous life. I honestly can’t think of a scenario where a PLL would be a more appropriate solution, unless I don’t understand the context. Perhaps if you were trying to recover a tempo from an actual note stream, rather than a tempo signal …