20 week waiting period - when does it start

[Whatwillbe2025]

Hello, i have applied for divorce and have received the email back below.
does the 20 week wait period begin on the day we apply for divorce OR once its been confirm that our application has been accepted.

Thanks a lot

I think it's 20 weeks from the date it was filed. My STBX solicitors filed last week but I haven't yet been served.