Am I understanding dividends ex dates right?

Hey, very new to trading. I had a question about the ex date and date of record for dividend payments.

As I understand, you get a dividend payment of you own a stock from the ex date until the date of record. Currently Chevron has an ex date on the 18th and a date of record on the 19th.

So, if I buy Chevron on the 17th/18th, and then sell on the 19th/20th, I get a dividend payment?

I ask because another company (Gladstone Commercial) has an ex date on the 22nd and another adjacent date of record. It seems like you could make money just holding shares of different companies for three days at a time. It feels like if it were that easy, everyone would do it. Am I missing something?

Thanks for your help and I appreciate your patience with what probably seems like a simple question.