30 minutes prior to scheduled departure is the minimum. Recommend arriving an hour prior to scheduled departure. Some days when Allegiant, Delta and United all operate at the same time, the lines at security can be massive (~70 people on Delta plus ~50 people on United and ~180 people on Allegiant is a lot of people in a smaller airport).
Allow more time than you think you need and bring a book to read... I generally arrive an hour before boarding time (not departure time) and that gives enough time, but take Paul Read's advice and check to see what other flights (especially Allegiant!) are leaving around the same time and allow even more time...
It takes no time at all...30 min max, usu more like 5. The ticket checkin takes longer than security at that sirport
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