Are "Days" on Fiverr Calendar days or Business Days? And can it just be hours?

[boldandbusted]

Howdy. I'm new to Fiverr and only recently put in real work into making a go of gigs. I'm a (computing) Systems Engineer/DevOps Engineer. I've got some interest from a prospective client. While the client's goal is not impossible, it is brittle and complex. I'm not confident that their end-goal can be delievered in a set of calendar days, but could likely be delivered in a block of worked hours. The reason for this is that there will be likely back-and-forth communication and considerations by the client's internal engineering teams on what I propose at each step. (I'm also creating Milestones).

My question is - are there any alternatives to what seems to be the standard calendar days delivery model at Fiverr? Can I actually negotiate that with a prospective client? Or is that system automatic and outside the control of the buyer and seller? I hope this makes sense! 🙂

Thank you in advance for your considered answers and proposals!

EDIT: Or, can there be an option to say "The work will be done when it is done, but no longer than X days/months."? 🙂

Edited September 13 by boldandbusted