Unlimited duration of new single work permit

Hello all
I am a student in belgium and i have been doing part time job since 1 year.
This august 2019, i asked for permit unique via my employer. My questions are:
1. Chances of success for getting permit unique as a student?
2. My employer demanded unlimited duration single permit. Does any one know any example in which government is issuing or issued unlimited permit unique in a case like mine?
3. Processing time of permit unique applications