If I remember correctly, you have MTU 8v183's. If so, I would not run them on the hard like that with raw water pump disconnected. I think you'd be better off rotating them with the stop switch engaged to move oil around without letting the engines fire. As for running them in the water. I'd rather run all of the engines on yachts I manage 30 minutes or more at the dock than 30 seconds. I run them for a good while until coolant temp rises to 140F or so, then run them up in Neutral to 1500 rpms for several minutes, then slowly bring them down and let them idle for 5 minutes after that, bump them in gear a few times. I haven't had any turbo issues, or any negative oil samples after doing this on many yachts for many years, and the exhaust temp gets over 400F and oil temp does get over 180-200F generally on the ones that show it (MANs).