I read the following from a journal article:

'Clonidine is a centrally acting alpha-adrenergic agonist with onset of
action 30 to 60 minutes after oral administration, and maximal effects
are usually seen within 2 to 4 hours.'

My question: is the starting point of '2 to 4 hours' the moment of
'oral administration', or the 'onset of action'?

In math:

(0 minute) +  (2 to 4 hours)

Or:

(0 minute) + (30 to 60 minutes) + (2 to 4 hours)

Thanks.
Dalei