AbdulMoizFarooq:
I am not sure, what is the minimum time I can get??
Write a short program to measure the time. I think an analogRead() takes about 100µsecs (see the datasheet) but you may not be able to read two different I/O pins at that rate
And given that I do get a (very) small delay between readings, then after 20-30 rotations, the values (or graph) of the sensor readings will be far off (definitely will not be in phase)...
The gap between the two readings will always be the same. Whether the pair of readings remains in phase with something that is rotating depends on how you sync the readings with the rotation.
...R