The afore mentioned Tecumseh manual also says 90 minutes for a large OHV single ( 14 to 18.5 Hp )
If you downloaded it then you would have noticed the * in the margin alerting you that it "might require R & R" so that adds another 60 minutes so now you are at 2.5 Hrs .
The companies down here who repower ride ons charge 4 hours for a strait engine swap, more if some "special fitting required " .
Stihl bless their helmet wearing hearts allow 15 minutes cleaning + 20 minutes for diagnosis .
The Stihl one is near impossible to work out because it breaks down the labour into tiny sections
Remove starter , remove blower, remove carburettor on manifold, remove carburettor alone etc etc etc.
It is a good idea when billing out your time to semi itemise
So if the mower was filthy and the owner brought it in for a service , rather than a repair
They get 1/2 hour cleaning the 1/2 hr diagnosis as the first 2 items in the labour section
The last item is always "test mow x minutes OK " , 1/2 hr for walk behinds & 1 hr for ride ons .
I am sort of lucky like this because the work shop is on a farm and I use customers equipment to do most of the mowing .
I get a lot of repairs in where the customer took the mower to a workshop, got it back & it was still not fixed.
Even then I get caught out
Just finished a warranty repair on a Billy Goat vacuum.
Ran a full tank through in the yard without a problem
Customer took it home &ran 5 minuets then it stopped
After multiple pull downs it finally twigged & I got him to bring the bag so the engine was under load .
After 5 minutes sucking up grass clippings from a pile waiting for composting it stopped .
Then undid the fuel cap and heard the big suck , a bad fuel cap
Prior to that it sat in the yard and ran through 2 full tanks of fuel without a hiccup .
So if you are being charged 4 to 6 hours that would not be unreasonable
Same if you are billing the time out.