I like to check in with the HM shortly after arriving at the theatre about anything that might be unusual about the show that night- a special event in the building that day, a post-show discussion, who's doing the curtain speech (if it's live), etc. This also gives them the chance to let me know about anything unusual on their end (they are shorthanded on ushers and may need an extra minute to get all the patrons seated, for example).
When we are set onstage (all props preset, in the correct light cue and sound cue, actors done warming up and clear of the stage), I turn the house over to them, usually right before half hour. They let me know when the house is open, and then I check in with them around 5min before curtain to see if they are expecting on on-time start. They check in with the box office to see if there's a lot of tickets at will call, or a big line at the box office, and let me know if they need to hold the curtain. I stay in pretty close contact with HM in the few minutes before curtain, and once they close the doors and turn the house over to me, I know we are clear to start the show.
I give them a standby for late seating, and then give them the "go" to late seat. If they need an additional late seating break, they can contact me and I will find a good (least disruptive) moment to do so. I also like to give HM a 5-minute warning on the end of each act.
All of this can vary widely from theatre to theatre- some theatres have very specific FOH policies that you need to follow. (Some of them late-seat throughout, or don't late-seat at all, or routinely start at 5min after the scheduled curtain time). I find it helpful to check in with whoever is in charge of HM before public performances begin about how things will run. I also prepare a document to give the FOH personnel about the show. It lists running times, approximate late seating break times, and any information that will affect the FOH staff. This includes things like if there is a pre-show fight call, or a gun is fired onstage, or actors enter through the audience. I find it really helps to check in with a HM that hasn't worked the show before to make sure they understand everything that is on the sheet.