Oh! Me sir, me sir! I know this....pull it back until it breaks, and it's an inch less than that!
But seriously, if you take the working length of the longest limb, that should be safe (or half the bow length with the 'no stiff handle')
My 50" Ash Cherry bow smashed just short of 25" but was shooting fine at 24", I'd expect a 1" safety margin as a minimum.
I've just measured that bow, the working length of the longest limb was 22". The Ash back failed in tension, there was a bad spot in the glue up too.
I've not used Osage, so I could be talking out of my nether regions.
Hope that helps.
Del