I haven't produced or edited a TV spot in decades, so I am unsure of something very basic: Is it standard practice to fade to black at the end of the spot or to keep your last image up till the very end and expect the fade to be accomplished by the master control switcher?
And if you do keep the image up, do you stop right at 30 seconds or leave it up longer?
I'm actually editing a 15-second public television underwriting spot, in case the practice is different for these.
I doubt that any MCR switcher would add a fadeout to anything. In many facilities, MCR is highly automated. Your spot is an element in a playlist. At the appointed time, source plays out of server, goes to air. At the end of the logged time slot, next source plays out, goes to air, without human intervention. If you want a fadeout, put one in, and, as suggested, finish it a frame or two early so it really goes fully to black.
My general practice is to put a 10 to 15 frame fade at the end, but in some very tightly-packed spots where you want the graphic up for every frame to enhance readbility of some text, or you get a client who says "I paid for those 15 frames, I wanna use them", then I go exactly to 30 and cut to black. I've seen spots on TV do both, many times, and yes sometimes the ends are cut short due to the automation setup, sometimes not. I figure most automation setups do add a crossfade anyhow these days. Never had a spot rejected because it cut to black instead of a fade. Nor for not fading up at the front.
In no case would I deliver a spot deliberately longer than 30 seconds though, fade out or not.