Work Permit Type B : Change Job

I work in Brussels with Work Permit Type B, which still valid until next February still valid for (5 months)
But I will change my employer and I will work for an other company

my question is :

Did I can work directly for the new company until the date of renewing of my work permit or I should change my work permit firstly to be for the new company then I will be able to work their

Your new company must apply for a new work permit for you. WP Type B is tied to an employer. You cannot work for another employer using a WP you got by your current employer.

- how long did it usually take ?
- did I need to return back to my home country and get a new Working visa  and stuff like that or just during my staying here the work permit will be renewing and just update my ID

if you search the forum with keywords like work permit and change employer, these questions were discussed many times already and you will find your answers.