The daily pass must be bought on the calendar day of arrival in Jurmala, and payment can also be made after entering the city. The pass is valid until 23:59 of the day of buying. Entering and leaving during this time can be repeated.
If you forgot to purchase a Jūrmala pass, you can do so for the previous day on the Jūrmala website: https://www.visitjurmala.lv/lv/pirkt-jurmalas-caurlaidi/