I think the exact number varies, but yes, you need about 500 ad impressions to expect that first cent, at least for a comic. I've heard some people needed more than 750. I wouldn't stress about it, If you get $0.01 per month and you need $25 to make a withdrawal, it'll take over 208 years to make that money.
I've made $0.40 through ad revenue so far, and I've been monetized since July 2024. That's ~9 months, and I had nearly 30k regular views in that same time period. Hope you didn't plan on making any real money via ads! Probably only the biggest comics make any money that way, if even then.