This is intentionally set up this way. Stacking instas can be incredibly powerful and should come with some sort of drawbacks. 

For this to work I think we'd have to nerf instas in some way to compensate. 

Instas are also used to quickly get a gun back if you lose one, or it is taken from you. 

We could allow you to choose when to use them, however, to offset that it would have to only give the rewards as if you used them at the rank you earned them at, or your current rank, whichever is less, and if they would have counted towards earning back a gun at the time or not.

Meaning, an insta petty earned/used on a don gives much less than an insta petty earned/used on a gangster.

Right now people can save them up and deploy them all at once, and I am OK with this because they have to sacrifice by not being able to petty while they are 'holding onto them'.

So if we remove that downside which helps balance the equation, we need to introduce another to replace it - keep track of when it was earned and what it would give you if you used it at the original time it was earned

If the collective is OK with this, then we can set it so you can use them whenever you want.