It's currently 5:36 PM EDT, so you are already in the PM (post meridiem) time. If you meant how long until 12:00 PM (noon) the next day, that would be:

• From 5:36 PM today to 12:00 PM tomorrow:
  • 6 hours and 24 minutes until midnight (12:00 AM)
  • Plus 12 hours from midnight to noon
  • Total: 18 hours and 24 minutes

If you meant something else by "how long until PM," please clarify!