Story related,
cannot be missed.
*Edit* It seems that this heist can indeed be missed, so make sure you complete the heist when it opens up.
*** Spoiler - click to reveal ***This heist will have you robbing a bank out in the boonies. As usual, things will not exactly go as planned. After the set up which has you staking out the bank and robbing a military convoy for some as yet unspecified hardware you will start the mission in a van and have to travel to the bank. Look out for some hilarious dialogue during the ride.
Once you are in the bank, thing will progress more or less automatically. I will not describe it in detail as that will take all the fun out of it, sufficient to say that you will get to use the military hardware that you stole. The rest of the mission should be very familiar if you have ever seen the movie HEAT. Run'n'gun, keep moving as quickly as possible, remember to use cover wisely and you should have no trouble.