Depends on how you define instant. If it's around 4-5 years, then yes. If by instant, you mean a couple of months/a year, then NO, it's NOT!
No doubt Bitcoin price can sky rocket at any time but it would still need a couple of years to appreciate and generate enough revenue for you to become a millionaire. However, if you just wanna sell it for smaller profits, then it could be a good investment option for you IMO.
The reason why it is called instant, it is because it is you can get the desired item automatically you put your interest on it, so it does not mean years, it does not mean weeks or months but instantly, or automatically.
And the time where you can be a millionaire in investing on bitcoin has ended, we are late 8 years ago to invest if we want to become a millionaire. Unless you start to become active in these forum and joined a lot of ICOs and Bounties, you may have a chance.