I do 28 hours in 3 days and my best friend (different employer) does 30 in 3 days. It is hard. TL:DR: it’s a recipe for burnout, especially if your DH works away and you’re also picking up everything at home during the week. I would strongly advise doing 30 hours over 4 days with a day WFH - potentially a shorter day - or looking for a different job.
You often end up working hours when there aren’t many others around so it can be harder to react to things in a timely manner or get others to respond to you quickly. The long days do mean you need quite a lot of energy as you have no wriggle room to think you’ll just come in early and pick it up the next day. You really need to think about food if you have any level of commute and taking all your meals to work, otherwise you end up grabbing unhealthy stuff or eating really late, which is bad for your digestion, especially if you’re straight into bedtime on arrival. As you don’t have time to exercise other than at weekends, it’s not great for managing weight, especially if you’re also sleep deprived.
I find it gives me a lot less flexibility if I need to leave early or come in late, in terms of making up the time. I’m also too knackered to do anything other than work on those days and I need the non-working days to keep on top of things at home.
You would need to think about the logistics of pick ups and drop offs - you’d be looking at a working day of something like 0800-1830 once you allow for the legally mandated 20-3 minute break if you work in excess of 6 hours in a day. Factor in any level of commute and basically you don’t see your children (if young) on the days you work, or you come in just as they’re going to bed.
Be aware that some public sector employers are changing WFH policies and may change goalposts for business reasons.
I’d also say that if you have two DCs, you’re probably not far off primary school and it may not be sustainable with primary school age children and a second parent not around during the week. So I’d really think about your options. Professionally, it’s much easier to work 4 shorter days. Personally, it’s much easier to be at home 2 days a week. Let me know if you find the magic answer!