Work Permit LTR

I have a query. I was initially on a student visa and then had obtained a work permit visa. I had applied for my Leave to Remain in the UK, three months after my work permit was approved (which was before the expiry of my previous LTR as a student). As per the Home Office regulations, I understand that once a student has completed a course and has limited leave to remain in the UK, s/he can work full time until their leave to remain expires.

My query is that, in order to qualify for an indefinite leave to remain in the UK, is the five year work permit period considered from the date of approval of the official work permit application or from the date of approval of the leave to remain in the UK, following the work permit visa application. Can you please clarify the same ?

Many thanks

Deep