Thoughts on the best time to buy ethereum during the dip?

So ethereum at $3700 is super appealing. I’m about to buy my first coin but should I buy in chunks as it goes up and down? Should I just buy 1 whole coin at once? Does anyone think it’ll dip more? I’m using Robinhood to buy because of the no fees thing but also have Coinbase. I’m new to Coinbase so I wasn’t sure what the differences were between these platforms.