You can definitely allow clients to book on the same day of the appointment! You can even adjust this setting by service. Start by logging into your vcita account on desktop. 

Default Same Day Booking

1. Navigate to Settings > Online Booking Options.
2. The Advance Notification setting on this page is the setting which controls how close to the actual appointment time that the appointment can be booked. For example, if the Advance notification was set to 24 hours, then you would only allow bookings to be made with a 24-hour notice - so, only for the next day. Adjust this setting to a smaller duration to allow same-day booking. The smallest allowed is 15 minutes.
3. Your settings will save automatically. 

Same Day Booking for Specific Services

To enable same day booking for only a few of your services:

1. Start in Settings > My Services.
2. Edit the service settings of the required service.
3. Scroll to the Booking Options setting. 
4. Click Customize if you are using default.
5. The Advance Notification setting is the setting which controls how close to the actual appointment time that the appointment can be booked. For example, if the Advance notification was set to 24 hours, then you would only allow bookings for this service to be made with a 24-hour notice - so, only for the next day. Adjust this setting to a smaller duration to allow same-day booking. The smallest allowed is 15 minutes.
6. Click Save at the top of the screen to save your changes.