Maybe instead of immediately jumping to a large ROH (say 1" or greater) that a competitive figures skater would use, you should be conservative and increase the ROH incrementally.  E.g., start at 1/2"; if you're comfortable with that, then go to 5/8" when the next sharpening is due; ....

As mentioned already, the tolerance towards dullness of the edges is a personal preference.
Many skaters are under the impression that edges are not allowed to slip. But controlled sliding is part of skating.
Dull edges have a bit the same effect as a more shallow hollow: you have no choice but to learn how to control your edges more effectively.
I sharpen my skates once a year, mainly to get the nicks out.

I've also tried several proxy methods.  To test for a sharp edge, I've used the fingernail test.  Even more sensitive for me is the fingertip test. If I run my fingertip across (not along) a really sharp edge, I can feel it and also see traces of shaved skin fragments left behind.  This works only if my fingers are thoroughly dry.

I also have a HDI (Hollow Depth Indicator) gauge, in which I swapped out the stock dial indicator for a higher-resolution digital indicator.  I thought maybe if I tracked the decrease in depth of hollow as the edges wore down, I would get a proxy for when sharpening was due.

None of these methods were successful.  Mainly because I touch up my edges with burnishing rods.  So I can maintain a sharp edge, but the edge angles vary and the degree of bite varies.

So ultimately I know it's time for a sharpening, even after repeated rounds of burnishing, by actual performance (starting to slip).  For me, primarily reduced control on back cross-overs and entrances to one-foot spins are the early indicators.  I do keep a log of hours of skating after a fresh sharpening.  But it's only a rough guide, because it depends on what moves I'm concentrating on:  different portions of edges get worn down more quickly than others; and different portions of edges are more critical than others.

My main coach used the fingernail method and assured me I was good to go still with 80 hours on my first ever sharpening.  I also have never found it to make any indication compared to how I felt while skating.  Perhaps my nails are soft (they are,) but it just never seemed like a useful test.

I routinely have gone that long between sharpenings, but I do enjoy the secure feel if done by a bit over 40 hours.  Even if I had the option for 20 hours I’d be reluctant in order to save blade longevity since I guess I can get away with the handling.  My main coach hasn't had his blades sharpened in over two years now but has great edges.  Dullness forces you to use pressure.
Without a trusted tech here I went from June to February without any sharpenings (  )
It’s a very personal experience thing as far as sensitivity to sharpness and how it feels.

As to the question… I find a careful look will tell.  You just see the obvious nicks and general lack of sharpness in the edges or in how light gleams on them.  Obviously I am a not scientific minded person but go by senses.  I bet Kaitsu and BillS will have more precise answers. 

The new boots are fantastic!   
I skated a couple hours and decided to use them for the competition already.  I actually never put my old skates on again since trying out the new ones.  I thought they were comfortable these days, but with the new pair it’s hard to imagine using them anymore even on ponds or in slush. 

Once I had my preferred laces in they were great.  Coach Cheerful said I skated better in the new pair, and I thought so too.  I felt like I was more in contact with the ice (especially in my heels for some reason) and had better control once I was used to the slight difference in feel of the blade placement.  Spins suffered for sure but began to come back alright with time. 

Despite the 3 layer super stiff construction I could flex happily quite quickly, and I am sooooo glad I didn’t go for a reduced level.  The woman that got gold in our adult silver category was really surprised I was competing in such new boots.   

I probably should have just had the backstays in the same grey, but I am undecided about that.  I adore the grey suede so much.  It seems to mostly read as pale tan in photos or videos.  That’s kind of perfect.
The tech at the shop was surprised by the half lined tongues saying he hadn’t seen that from them before.  I found it odd also, because I thought my inline pair only had it done that way due to it being a retrofit.  I’d guess that it is something done to allow for replacing foam in the long term viewing it as a seamstress.  If the lining leather isn’t stitched down and full length then the tongue padding can be replaced without taking the whole piece out, and that makes sense.

Despite only about 3 hours in them the chem glaze wore off in a spot from lunges on the left sole.  Water clearly leaked in where Too Sharp added more screws also, but not where the other tech placed screws.  I melted beeswax there and hope it’s okay now.  The glaze has a bit of hairline cracks and seems thinner, like I saw on some other pairs, but my original pair had a lovely robust glaze.  I hope it holds up better than I fear. 

I’m already dreaming of ideas for another pair… whenever that might be.  I’d like them tall like old school boots and in white pebble perhaps?     There’s plenty of time, hah!  I think some design with crystals where Harlick does the custom cutouts might be nice.  The crystals are my favourite part aside from the suede colour.