Does Groww allow BTST?

Yes, Groww allows BTST orders (Buy Today Sell Tomorrow) that enable you to sell the stocks before you get their delivery in your Demat account.

As a general rule, the trades follow a T+2 settlement cycle. Hence if you buy a stock today, the shares get credited to your Demat account only after two days starting from the T-day post which, you can sell them. However, BTST allows you to sell the shares even before they get credited to your account and thus enables you to take benefit from the short-term price volatility. It is also important to note that BTST involves the risk of short-delivery for which you can get penalized by the exchange.