Offer recd! Time before move?

I have received a job offer and accepted the same with QP. I have been  informed not to resign from my current job until I hear further from QP in writing after Medical, Immigration aspects  are cleared are sorted out with authoriries? 

Wated to know as to how long is the time gap between accepting offer and clearence? (Weeks/ Months???) before I can move to Qatar?

Thank you.