How Long Will It Be?

Yesterday’s Problem:

The letters O, T, T, F, F, _, _ are part of an
intelligible series. Add two more letters in
the blanks.

After you do this, explain how the series can
be expanded indefinitely.

Answer:

The answer is “O, T, T, F, F, S, S for One,
Two, Three, Four, Five, Six, Seven” and so on.

Today’s Problem:

The doctor gives you 3 pills. You need to take
one pill each half-hour. How long will it
be until you are finished taking all three pills?