My both Speedy with 1861cal. last approximately ~50-51hours. First of all, are you sure you wind it fully until it stops? If yes, when did you buy your moonwatch? Is it time for a service?
I believe Omega specs say 48 hours. Do you still have warranty? 18 hours isn't even close to what it should be.
Agree with @Celestron, 18-20 hours should just be before halfway through your reserve. I would have it looked at.
I don't really know how long the winding of my watches lasts. I rotate through my watches every day, so they are still running the next morning but I'm on to the next watch by then. Plus, some of my watches don't wind at all, such as the Seiko skx007. Strangely, even though it is an automatic, it only powers up by motion and winding the crown does nothing for it. .
I'm not sure but I believe magnetized speedmasters can often also have a drastically lower power reserve.
Can't be that important, OP hasn't been back since he started this thread! Mine's wound daily, so never stopped in my ownership, certainly longer than 18 hours though
On the contrary, after reading the responses, he immediately ran to the AD to have his watch serviced. He'll be back in a minute.
That's the way they were and have been like that for many decades. Whilst convenient in a few instances(like when it's getting very near service time) a manual wind function is relatively redundant on an automatic. The Seiko auto wind mechanism is said to also be efficient.
The thing is. Has it been ascertained whether the OP was running the chrono continually. He's obviously new to it all and it wouldn't surprise me
For a watch in good condition it makes a few percent difference; not more than 50%. See https://omegaforums.net/threads/my-first-watch-and-its-an-omega.116749/#post-1550811