Is there a easy way to measure accurate time between 2 pulse on the 101?
That depends on the interval between the pulses. If they are a week apart, measuring the time to +/- 1 day is trivial. To +/- 1 millisecond isn't much more challenging.
If the frequency is more than once every 4 microseconds, then it becomes more challenging. You have to count a number of pulses, then divide by the time you did nothing but read pulses.