How to set a random delay between messages?

I’ve looked at this pages:

And you can set a pause between messages, but I would like it to be random, like for example, between 60-200 seconds between individual email sends

Kind of like Gmass does it from their UI as demonstrated in image below:

I understand the question, but what’d be the desired effect of setting a random intervals? Have you experienced any issues with regular intervals?

Random gets you better deliverability, looks less like a machine, when you send message too fast or to automated, Google doesn’t like it.