In my opinion, the first time meeting a provider, I like to make sure that everything is confirmed, but usually the day before. For the providers I've seen before and I'm friendly with, the confirmation is not necessarily needed, but with some, there are flirty emails all the way up to the meeting.
A few personal stories on the subject:
My first experience almost didn't happen because I was at a place that did not allow cell phones and the provider called and emailed me to confirm a few hours before our appointment. Luckilly, I was able to respond before she cancelled the appointment. This appointment had been set up for a few weeks, but no confirmation was done up until a few hours before. Being brand new to the hobby, I would have made sure I could have accessed my phone or confirmed the appt myself earlier in the day.
The second happened last year. I had made an appointment for about a month in advance for a well reviewed provider and I was hosting (putting up the money for the hotel). I confirmed about a week before and was told everything was okay. The day of the appointment, when she didn't show, I called, emailed, texted, contacted through various verification sites and got no response. So, I was out the money for the hotel because we didn't confirm the day before. Turns out she went on a personal vacation and totally forgot about our appointment since we had made it so far in advance. She told me that she would discount a future appointment for half of the hotel cost, so we'll see.
Lastly, there was a visiting provider who told me that she'd be able to see me and asked what day and time I'd like to meet. I told her when I'd like to meet, which was about a week away, and asked her if that worked for her. I never received a response from her, so I just assumed that there was no meeting. The morning of the date that I requested, she emailed me confirming our appointment for later that afternoon. I told her that since I hadn't received a confirmation from her, that I didn't think we had an appointment and that I was spending time with my family in another state. She cussed me out saying that guys are so stupid and impatient if we don't hear back from the providers right away. She had a week to tell me that the time I requested was okay. I didn't need a huge response, just saying, yes, that's good for me, see you then.
So, all in all, I think a confirmation the day before is sufficient for both parties. I know last minute things come up, but that's why they're last minute. That could happen with a 24 hour confirmation or a 3 hour confirmation.