Untested In Multiplayer, Should Work Fine, Report Back If It Does Not
Welcome to the age of "Takers" rather than "Givers" where no one can give up 3 seconds of their time anymore to actually be constructive in life

Does exactly what it says on the tin.
If you can easily rifle through your coat for your mask and yank that shotgun out of your jock strap in two seconds flat... why can't you put it back?  Now you can.
This gives you the ability to put your mask and weapon away after taking them out, outlandish concept, right?

Instructions are simple:  Just like putting the mask on, hold the "Deploy Equipment" button.  Instead of placing your equipment on an invalid surface, you will begin to hide your mask and weapon.  If you are actually facing a valid surface for your equipment, you will default to placing your equipment.
This means Armor Bag users are out of luck, however if you have the Jack Of All Trades Skill to swap your equipment, you can swap to the other equipment to get around this.  Consider it as you're already carrying a massive bag of armor plating that trying to hide it again would be unreasonable.

Note 1:  The normal stealth "casing" notice will purposely not display again if you unmask, that way you are able to see the hostages and other information you may have displaying, it is your job to remember things are still quiet.
Note 2:  Other players will only be notified of the normal action progress for putting on the mask, there is no such countdown for others when unmasking.

Since this bonus is fairly powerful to stealth, to keep things fair, you're stuck to the following logical Desired Behavior:

• You will only be able to unmask if you normally could have your mask off  (Can: Bank Heist, Cannot: Aftershock)
  
• If you take any decent single amount of damage to armor, such as from gunfire, from explosions, etc., you will be unable to unmask due to having "visible damage"  (This does not apply to falling, a bit of a fall wouldn't leave much of a scratch)
  
• If this damage instead rolls over to health, you will be unable to unmask  (Getting shot in the face is pretty visible)
  
• If you ever end up bleeding out, including from falling, you will be unable to unmask  (Again, broken legs are pretty obvious)
  
• If stealth is completely broken, you will be unable to unmask
  
• If you are doing any action, such as changing weapons, carrying a bag, riding a zipline, etc., you will be unable to unmask at that time
  
• While unmasking you will be unable to move  (As trying to meticulously hide everything would take time and effort)
  
• Unmasking will take 4 seconds  (Double the time to equip)