As soon as the cop gives me the ticket for speeding.

My clients all know I am always early, so if I know I will be late, I call as soon as I know. 

 ASAP.  I call or text to verify my status. 

The minute I realize I might be late, I let them know.

As soon as I know or get in my car.

William - I let them know as soon as I possibly can.

I call as soon as I realize that I might be late.

As soon as I know that it cannot be avoided.

I let them know as soon as possible.

I first apologize to my clients for running late, and I  tell them what has caused me to be running late.  I also give them my estimated time of arrival.

As soon as I know there is a possibility.

Never seems to be an issue for me as I am an old hand at proper scheduling and keep my buyers on schedule.

soon as I know...they know

I try to be realistic,  but then again if its a showing appointment, I allow for a buffer of time, so doesn't happen often.

What I find is that I sometimes get ahead of schedule, makes things complicated then. Only happens when a buyer says "no" to seeing a home upon driving up. 

William Feela With all the traffic problems here, I will call them from the car if there is a traffic problem.

ASAP...No excuse not to call

We schedule in 2 hour time blocks.  That allows us to never run late.

When I am showing houses and buyers are late, I let the listing agent know as soon as I find out.

I keep the party moving and never run late-ever.

 Good Sunday morning William. I let them know as soon as I find out that I'm going to be late.

Good morning William. No matter how much time, I would most likely add 15 minutes.

Right away, if I know I can not make on time, I'd text right away and update often. 

Between 20 and 30 minutes William Feela 

If you mean when showing homes I am in the window and I give window times and not specific times.  I let my buyers know we must keep appointments, it's never been an issue

William Feela usually long before even they start for the appointment.

William, 

I call 10 -15 minutes ahead of time.  A

I call as soon as I realize I'm going to be late.

As soon as I can. I do my best to never be late.

I always plan to be early. That's just the way I am. 

William,
Generally speaking ASAP but sometimes I wait a few minutes if it will help me be able to tell them when we might arrive.

As soon as I know I'm running behind ....unlike going to the Doctor ....LOL

As soon as I'm off schedule I let the next client know. I give them the new ETA or the option of rescheduling  to be sure they get the full time their situation deserves.

As soon as I know I'll be late.  Even if it is just 5 minutes.  It's a respect thing.

as much ahead as possible.... even if I think I might be a few minutes late, I'll make sure they are aware.....

I'm habitually early, so if I'm caused to be late because life happens, I call and let them know what the GPS estimates + 5 minutes pad. On a few occasions, I have gone to call a client and tell them I'm late, when suddenly they call me apologizing their running late...wheew! Then I'm back to on time without having to confess! 

As soon as possible. Hopefully at least 10 to 15 minutes ahead of the appointment.

I try to plan my day so I'm not late.  I was running behind once. I phoned them as soon as I could.  It worked out ok, they walked around and checked the outside of the home while waiting for me.