I had this same issue. My stbd motor was rebuilt by the PO. Injection pump was also rebuilt when he had a hard time starting it after the rebuild. He subsequently replaced almost everything on the motor trying to get it to start like normal. When warm, it would start right up with no issues. When cold, it was horrible. 45-60 seconds of cranking to do anything (not all at one time). And when it did start, the RPMS would cycle up and down about 400-500 rpmps until warmer. Brian at AD recommended throwing a set of block heaters in my motors and not worry about it if it started so well when warm.
After reading this thread late last year, I looked at my adjustment. Turned the adjustment further out about 5-6 turns and it started right up. No issues at all. I ended up taking about 8-10 more turns out of the adjustment and now it starts as soon as I hit the starter button, even in winter. Just don't adjust so far that the solenoid does not kill the motor when needed.
The PO literally slapped his forehead when I told him that. I think this is an adjustment that not many think of, or even know exists.
"Everything on your boat is broken.... You just don't know it yet."