LM2854: maximum value for soft-start cap

I cannot think of anything specific that would limit the SS time. So I do not think there is a theoretical maximum for the SS capacitor. I can tell you that 99% of all applications I see have SS time requirements from 1 to 20 msec. If you use a large SS capacitor, be careful about quick restarts. The SS pin discharges internally thru 5 k ohm resistance. Your proposed SS circuit will have 73.5 msec time constant, so you will want to ensure the circuit remains disabled long enough for the SS cap to discharge before re-enabling the circuit.