how can set clock parameters ?

Hi , I am designing ADC for which I am giving clock signal, but I am curious about the parameter of clock signal that how can I set the rise and fall time of clock.

for example, with the following specs how much Trise and Tfall can be possible so that ADC can operate properly ?

Clock = 100MHz

Pulse width= 2.5n (duty cycle 25%)

Trise = ??

Tfall = ??

Actually, I want to know how much % of Trise and Tfall with respect to clock speed and pulse width. is there any ratio for this ?

could anyone please guide me with this query ?

Thanks