Not happy about the pills answer. Depends what you mean by last. Agreed that the 3rd pill will be taken after one hour but I assume the effects will last for another 30 m, so it would be 90 m later before you needed a fourth pill, i.e. the effect of the pills will last for 90 m.
Mike I interpreted "last" as meaning "how long would it take you to take all 3 pills in front of you" - not how long the effects of the pills would last.