Reloading too imminently

Hi folks,
I send a newsletter out to about 400 recipients and need to slow it to about 200 an hour (ISP rules). I edited config.php to do that and it mostly works, but… when it hits the batch limit (I’ve tried various values), I get the message:

In the last 300 seconds more emails were sent (18) than is currently allowed per batch (18)
Script stage: 5
Finished, Nothing to do
Less than batch size were sent, so reloading imminently

This reloads/repeats every second or so and eventually crashes the browser tab by using too much memory. I’ve tried setting up cron jobs but I just don’t have the technical knowledge for that. Is there any way to get it to just reload slower? Once a minute or so?

I’m using v3.5.8.
Thank you!