How exact are the times for how long to wait between pills?

Question

A 120mg pill of Sudafed (Pseudoephedrine hydrochloride), for example, lasts for 12 hours. You are not supposed to take another Sudafed pill before the 12 hours are up. **How exact is this 12-hour limit?** Do i have to wait at least exactly 43200 seconds between pills? How much leeway is there? Could i take the second pill a few minutes (5? 10? 30?) before the time is up? Note that Sudafed is used as an example here. The same should apply to any other drug with a time limit.

Answer 1

This answer can change based on the actual drug being taken or given and really should be a question one asks the Pharmacists. But generally speaking, if there are no restrictions, 30 mins-1 hour before its due is what you will typically see. However, always check your facilities policy regarding drug administration.