Hey guys,
was wondering: usually, how much does it take to get an answer after formally submitting for a PhD position?

There's no answer for that: it depends on your department, your application (how much supporting materials you included), the admission at your uni, etc… I would say from my experience don't expect a response before 8 weeks especially if you also applied for funding.

Yeah, that's what I've alse read somewhere online (at least 4 weeks, up to 8).

A lab mate told me she's sent an email asking for an informal feedback, the supervisor replied the day after, telling her to formally apply and the very next day after submission, at least that's what she says, got a call for an interview (it's not the same uni, but I got scared! LOL)

many thanks for your answer ;)