Hi @Atif Mehmood
According to the information on their website, it can take up to a year, in certain cases longer. They process the applications according to the order in which they receive them, i.e. they can not prioritise a particular application over another.
If you have not done this yet and are planning to do so, they advise to use the form they provide and to submit all the documentation they require. This can help to shorten the process.
Here (via online translation) is the information directly from the office itself:
https://***-brd-nrw-de.translate.goog/themen/schule-bildung/schulrecht-und-schulverwaltung/zeugnisanerkennung?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp#faq_12206
Best,
Éanna