This can be done by setting up individual ticket groups for each time slot. The group function can be found on the 'ticketing' tab in the 'edit listing and tickets' section of your event admin. You should click '+ ADD NEW TICKETS' and then '+ ADD TICKET GROUP'.
To help organise tickets, groups can be renamed by clicking the small arrow beside each group. Once the group has been added you can then then add ticket types within the group, for example: Early Bird Single / Early Bird Group.
After all tickets within the group have been added, you need to set the 'max tickets per event' this is vital to limit the number of tickets that can be sold within this ticket group.