I rarely do a same-day booking so usually email the wg in advance. I find that the better quality, higher class (and usually more expensive) WGs tend to be more organised and will respond with well worded emails, and then ask you to book a time via the booking system. If you book without ever talking to them they will usually just ignore you, or even block you.
The cheaper, lower class, ladies, tend to be less organised and ignore the calendar / booking system all together, and rely on direct contact via phone call. They might respond to emails, but usually they dont. Sometimes they will ask you to put in a booking just for feedback, but most dont care.