You can, but most likely the spa will be booked up. We always advise to schedule your appointment in advance by calling the spa directly.
If you purchased a hotel day pass and thinking of getting a spa treatment while visiting on your day pass, please contact the spa and schedule your appointment in advance. Most spas need an advanced notice to schedule you with the right specialist to get the best spa treatment you deserve.
Note, most participating hotels & resorts have spa facilities reserved for spa paying customers. Be sure to check the details on your day pass if your day pass allows you to use spa facilities without doing a treatment there. If you purchased a spa pass through DayAxe then you don't need to worry.