Say he's booked a date for Wednesday the 30th, a month in advance.
I'll tell him something specific, like: 'I'll be in touch on Tuesday the 29th to confirm'
Then, I'll email him Tuesday morning or early afternoon, 'Hi just confirming our meeting tomorrow at 9PM. Can't wait to meet you!'
If he replies, then we're on.
If he doesn't reply by that evening, I'd say, 'Hi, I still haven't heard from you about our meeting tomorrow at 9PM. If you'd still like to meet, please let me know by tomorrow at 12PM. If you've made other plans, no problem, but please let me know'
If he still doesn't reply by say 9ish the morning of (has never happened to me), I'd write again, 'Hi, I haven't heard from you about our date.' Then I'd reiterate that he needs to be in touch by 12PM, or I'll assume he's made other plans.
Around 11-11:30, I'd probably send one more message, just to cover my ass.
The key is to be very specific about when you will be in touch to confirm, and what deadline you set for assuming that the date is still on/not...
-- Modified on 9/17/2015 7:13:33 PM