Yes, it is quite common for him to take several days to reply. I've got two kits from him, and it was slow to get his attention, but once we started to get into details, he would often respond next day (instantly, essentially, given the time difference).
IMO his reputation here is well-deserved and it is worth the wait. But time-wise he is a victim of his own success, so my advice is to respect his time - wait maybe three days and send a gentle reminder. Use one contact method only (the emissions-free email seemed best in my experience). Make sure your emails are short and to the point. Offer to pay as soon as you know what you want.
350W cell_man front geared on GT Karakoram, 10S LiPo, max 30 kph, 6.5 Wh/km assist.
Second build: rear 500 W Mac on Raleigh Avenger, LiMn from doc's Makita packs
Ziggurat's beginner's info