I want to try some DeFi on BSC but every exchange I check either doesn't sell BNB or makes me wait days for bank transfer. Is there a platform where I can buy BNB with a credit card and get it within minutes?

I had the same problem. What solved it for me was using https://paybis.com/buy-binance-coin/ – you can buy BNB directly with a debit or credit card. Verification took under two minutes, and the BNB was in my wallet almost instantly. Fees are shown upfront, and you can buy up to $1000 without full KYC. I've used it for gas money on BSC multiple times. Way faster than dealing with exchange deposits waiting for clearance.