An example of instant is an answer received very quickly, an instant response.
An example of instant is oatmeal that has been pre-cooked and dried for very quick cooking, instant oatmeal.
At the instant of combustion.
Your letter of the 15th instant.
An instant need.
An instant cake mix.
Instant lottery tickets.
To demand instant obedience.
Yours of the 13th (day) instant received.