Not a problem. To update your availability: 

1. Go to Control panel > Edit profile > Availability or use this link https://app.getblend.com/profile#time 
2. Select your time zone.
3. Mark your working days.
4. To exclude specific hours, click on the day and select from the drop-down list: 
5. Click Save.

Note: during your unavailable hours, you will not be able to view new projects or receive project notifications.