Sorry to talk so long...
I was at a gala a few weeks ago (featuring no less than ten speakers). At least 80% of them began their talk by saying, "I know you're hungry, but..." or "I know it's late, but..." or "I know you want to go home, but..." and then apologized for giving a speech.
If your speech needs to be prefaced by an apology...
don't give it.
That's why they call it giving a speech. It's a gift. If you have to apologize, it's no longer a gift, is it?
Our collective fear of public speaking has created a host of awkward situations and events. It's pretty simple: Be brief. Or don't come at all. Don't do anything you need to apologize for.
(and brief means sixty seconds, usually. That's enough to say hi, to say thanks and to move on.)