For me, regular depends on many things.
Do we see each other every two weeks, or is your allowance/schedule only once a month? Or do you come to see me as soon as you get your quarterly bonus? I would consider all a regular of different types.
I personally don't offer half hour rates... but you are more than welcome to sneak in a quickie once you have become friendly with me and my schedule allows.
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My quarterly friend for example, always spends a couple hours with me. My biweekly is usually lunch and an hour. Some are even dinner/hangout/fuckery for an evening every week.
Some of my friends I have been seeing for 4+ years, some barely a year. In general, once I have a 3rd session with someone I usually get much more comfortable with them. We often spend time after the clock just chatting, having meals or sharing a beer and a hammock. Most of my long term friends I have built close genuine friendships with. Not just a paycheck, though, I have some of those too, who just choose to get in, get off, and gtfo. We have a different type of bond/relationship. Still enjoyable though.