This only applies for T2 things with the blueprint calculator.
You’ll find a new row in the Time Calculations box. This is called iskh 24H rounding
This is taking the time taken to manufacture all the runs for the invented blueprint, rounding it up to the next 24 hours (so a 3 hour run takes 24 hours, a 25 hour run takes 48 and so on) and then calculating the isk/hr as if that’s the time taken.
This is so you can have an idea of how much isk/hr you’re making, if you’re only putting jobs in once a day, at the same time. It’s not perfect, of course. If you have a window of several hours, then a 25 hour job probably won’t consume 48 hours of a slot.
But if you look at something like a Hobgoblin II then you can see how it affects your profitability if you’re doing a single run per day.
As it’s not relevant for non-limited runs, it’s not added for those.