no, it is not normal...I am a broker of 20 years and i am almost always on time. Granted, when I am showing a client multiple homes I have to give a time range i will be there, but I keep that to a 1/2 hour time frame.
Does it take some planning on my part? You bet, but that's what a professional does. In my experience as a long time broker, I can say in my area, only about 20% of the agents are truly "professionals" that are consistently doing thins the way they should be done.
You can bet these other 80% that treat clients like dirt would not allow themselves to be treated that way...and on my end, I have to often call these slackers multiple times to get a return phone call, and often the multiple phone calls still go unanswered.
And don't even get me started on real estate attorneys!
Unfortunately, if you want your home shown and you insist on being there, this is what you can expect. You could make the listing agent be there for all showings, and you should. You are paying for their service...make them service you, or find someone else who will.