Don’t go over your time. Ever.
Except, maybe, if they give you a standing ovation and refuse to leave the theatre, chanting “More more more!”
But in a business environment? A meeting? A presentation? No.
If you’re the senior person in the room, you are being an asshole and setting a bad example for your troops. If you’re not the senior person in the room, you might want to look up the phrase “career-limiting move.”
I am constantly aghast at how often business people blithely run 25 or even 50 percent over their allotted time. I worked with an NGO a few years back, selecting the new CEO. For the second interview, we included a 12-minute “my vision” presentation. In the briefing document we stressed that the presentation would be timed and that it was to be “strictly 12 minutes.” I told each candidate as they stood up to deliver: 

“Imagine you are delivering this presentation on CNN. Unfortunately, the satellite will pass out of coverage in twelve minutes’ time, cutting you dead. So you need to be really mindful of the clock. Go.”

Only two out of five candidates stuck to their time …
Execupundit, wise man and all-round seer Michael Wade nails it.
“… and I’d like to thank the Dolly Grip and the guy who brought me those little moist towelettes and my kindergarten teacher and …”