Are stocks available instantly after purchase?

I dont have any stocks, i am a volunteer with an animal rescue called Sanctuary Hostel and i got a notification from our donation platform that they are offering stock donation matching but only for the 29th which is weird but wateva

I have $900 in my fidelity bank that i transfered to the investor account section that i could use to buy a stable stock probably Amazon and then just donate it right away but i dont know if it takes time to process the stock purchase

I dont have an interest in stocks aside from doing it this time for the matching and im not worried about taxes as im on disability so all my income is tax free and the IRS said i dont have to file

Thanks