Hofacker wrote: how long do you have to wait before reaching for your gun?
Do yourself a favor and buy a snub nosed revolver or Kel-Tec P3At (or other pocket pistol). That way, you can put your hand on your gun inside your pocket and nobody will accuse you of "flashing". A pocket pistol makes a great BUG or primary carry gun, depending on your needs.
Or change your carry method. Keep your 2 top shirt buttons unbuttond and have your gun in a shoulder holster under your shirt. You can reach for your gun in your holster but your shirt is still covering your gun.
Wear a very small gun on a holster on a necklace.
Wear a holster UNDER your pants and tuck your shirt under the holster. You can reach for your gun and the gun will not show. It will only look like your are scratching yourself.
Belt carry with a shirt tucked over your holster is the worst method of carry if you want to put your hand on the gun in an iffy situation (you are not 100% sure if deadly force is warranted) because if you do so, you'll have to lift your shirt and you'll be "flashing".