Is there a difference between rise and fall time and modulation frequency
If a laser had a modulation frequency of 100MHz would that be the same as a rise time of 5ns and a fall time of 5ns as 100MHz is equal to 10ns?

No because if that was true the modulation signal would have the shape of a triangle wave.

If the modulation was a square wave then the rise and fall times would need to be much shorter.

If the modulation was a sine wave there would be no real rise/fall times.