Can't get this to do right either.
To enter duration, you have to settle for Omni's preferred (and somewhat ridiculous IMHO) method of displaying the info, as far as I can tell, though if you'd found a solution, please share?
If I type in 10m, OO displays it as "0.167." My complaint is not that this is technically slightly inexact (even though it is) due to rounding. Nor is the problem isn't that I'll forget that"0.167h" means 10m .The problem is that like many or possibly almost all people who estimate and record time, I want to view 10 minutes as something more like "10 minutes" or "10m." And if I share this outline with somebody, they'll want to know why I recorded time in such a weird way. Some people might not even know off-hand that ".167" comes out to 10 minutes.
And the summary totals are also awkward/weird I'm estimating time I'll likely spend on various projects for the day or week, and then I want to see the total estimate as the summary. The total estimate for today for all tasks today is, according to OO, "7.617h." OK, I know to round, so that's a little over 7 hours 30 minutes. But why can't it I choose to show time in a way that reflects how I and most people normally read, write, and think about time? BTW, 7.617 is technically 7 hours 37 minutes and 2 seconds. I did NOT enter seconds into any of my tasks, but due to OO's weird choices about what to round and what not to round, I get 4.617, which is both awkward to look at and, technically and precisely speaking, an inexact calculated total.