Hi,
You could sitch to another cron server that triggers your site more often, for example every two minutes. When you do so, please do not forget to disable the cron in Acymailing, othwerwise you will run into issues.
There's also a way to send multiple batches of 20 in parallel. For this you need to switch from Acyba's cron server to your own or a third party cron server. It's documented here: https://docs.acymailing.com/v/old/developers/multiple-queue-system
But before you put a lot of effort in this, please consider to migrate to Acymailing v7. It can send multiple batches by default and it's a lot easier to setup. Also, v5 is reaching end of life. That's why we really recommend to migrate your Acymailing.