I refuse to be pressured, even if I arrive early outcall I tend to wait until the time because I find I get greater respect from the client for doing so - plus I can spend the time answering messages, emails, catching up on admin, ordering more condoms or simply having 5 minutes downtime. All of then means I'm calmer and more focused on the client.
My experience before realising this was if I start shuffling start times around, the person will do it again and we end up with floating appointments, and a much relaxed almost casual attitude. Also rushing for an earlier than booked start can throw my routine, 6 months or so ago I set my personal phone voicemail to that of my sex work phone by mistake when agreeing to an earlier than the booked start time. By the time I rectified it, we were almost at the original start time and the new to me client had experienced my horror at realising my error.
If however an earlier start really suits me, and I can do it easily without upsetting my schedule or routine I will do so but this is my choice.