Hallo Arif,

on chip oscillators of mcu are designed in such way, that they will run with very most crystals arround. Look at burden cpacitance specification and connect to both XTAL pins correct burden capacitance. Mostly something arround 27pF...33pF. It's worth to have always a look at datasheet of mcu, because sometimes specifications can differ.

It's important for reliable start-up of oscillator that power-on time is not to long. Manufacturers often recommend a power-on time of less than 10msec. It's just the edge of power-on (fast Vcc ramp) which hits the oscillator and helps him to start-up with oscillations. Without the fast edge of Vcc, assuming a very slow start-up, oscillator is only possible to start from noise. So, stabilizing of oscillator needs much more time.
In seldom cases, especially when running mcu at limitations of temperatur range it may happen that oscillator does not start-up, at all. Then, making power-on-time much faster, can solve problem.

Kai