when does a "remain clear" instruction end?

Recently I was departing a small airport (with no control tower) which
was underneath the class C shelf area of a somewhat larger airport
(which is an air force base). Immediately before departing, I called
the approach controller for the class C airspace and told him that I
was departing and would like flight following. I was actually hoping
to fly straight over the larger airport (they weren't busy due to the
time). The approach controller assigned me a transponder code and
told me "after departure remain clear of the class C airspace". So
after I took of, I started flying a route taking me around the class C
area that extended to the surface. Well, the controller then called
me by my tail number and asked some questions (I don't remember
exactly what -- it might have been my expected cruising altitude and
aircraft type, I think he may have also said radar contact, although I
can't remember the specifics right now). As soon as this happened, I
turned and headed directly toward my destination, taking me across the
class C to the surface airspace. A fellow pilot was with me, and he
later mentioned that thought I might have violated the controller's
instructions. Hmmmm... That brings up a question --- when does the
"remain clear of class C airspace" instruction end? I figured that
since he called my by tail number and was clearly communicating with
me and didn't assign any vectors or repeat his direction to remain
clear, that it was now understood that I could enter. The controller
didn't give any indication that I had done anything wrong, but I want
to be sure that I understand this for the future. So ... if I'm told
to remain clear in the future, WHEN does that end?

Thank-you.