@New_Delta. There are a few ways to handle this.

#1. Keep USD cash in an exchange wallet. Coinbase has one. It takes 5-7 business days to arrive, but at that point you can trade instantly with it. I try to keep 5k in there at all times (just refill as I use) for quick trade opportunities. It does take time to send mt BTC or ETH to the exchange I look to use, so its not instant but we are talking minutes not days.

#2. for small sums ($300-500), I have been able to use a credit card for instant coin purchases. Not much for my volume, but its something!

This is so relevant right now as I wish I could buy heavily and I am blocked waiting for my BTC to arrive, curse you fate.

Your welcome @HodorHodl.