I have a visa that starts on March 15th and my flight arrives on the 14th at 11:30 PM. Would I be allowed to board the plane, as I am certain I will not be going through the immigration procedures until after 12:00 and it is already the 15th?
Would I be allowed to board the plane?
Assuming the airline doesn't make a mistake, you will most likely be denied boarding. Yes, this might not make sense from a practical standpoint, but airlines usually stick to the rules. So if you want to be safe, change your flight to a later day.
I will not be going through the immigration procedures until after 12:00 and it is already the 15th
If you somehow convince the airline to let you board the plane, this should indeed work. If you show up at 00:01 with a visa valid on that day, you should be allowed into the country. But unless you're willing to risk forfeiting your ticket, I wouldn't plan on doing this.