How long does now last, by the way?Process and nominalisation
Time is inferred from the change in the relationship of things in space. (Space in inferred from the relationship of things.)
Time and space are not things. They are inferred from things.
You asked “where” do we start. We start from where we are with this inferred time and space. Perception starts in this thing at this time and place.
To ask how long “now” lasts is the incorrect orientation to time, since time is known from the interaction (change in the relationship) of things.