The scariest time we had was at Cozumel when she had to do three minutes of mandatory time then three minutes safety and on the way up from safety she was penalized one more minute and had to go back down. Mean while we were seeing the boat ladder go up engines start and move then stop. The boat was anxious to leave because of the storm brewing at the surface but other divers on board (who we just met on board)realized we were not on board and warned the crew. This is when i realized that to conserative can have its pros and cons.
That's it in a nutshell.
When I went with a trimix computer I selected one on the advice of an experienced off shore diver who articulated the need for a computeer that is set you get you out of the water in near minimum time in the event you absolutely have to in case the weather blows up, etc.
You can always ascend a bit slower and linger longer at a safety stop than the computer advises, but you cannot tell a computer set on uber conservative mode that you really need to get out now as it will still consider it a violation.
My Cochran allows conservatism settings from 0% to 100% and on 0% it gets you out of the water faster than just about anything else on the planet. For recreational diving I tend to set it in the 30% range and then adjust up or down (usually up to 35%-40% to match the dive buddy's computer so I have a good idea where they are at in terms of NDL's.
In that regard a conservatism settings on a computer can be used to keep two different computers in the same ascent time required ballpark instead of having two that differ greatly.
On decompression dives, my computer is a back up to a computer generated plan on a slate anyway so I set it at 10% to give me a pretty fast trip to the surface if for some reason I have to abort the dive and need to surface quickly or if the weather is closing in.
On many computers, you have a tissue loading bar graph that allows you to see where the controlling compartment is in terms of a red zone (deco), yellow zone (caution-but ok to surface), and green zone. If you have one, you can leave a computer offering adjustable conservatism at a liberal setting and then build conservatism back in by slowing your ascent and adding some time with a slow ascent from 20-30 feet with added time at the safety stop to let the tissue loading bar graph get farther down into the yellow or even into the green.
That approach, combined with using conservatism settings primarily* to match a much different computer in use by a buddy makes more sense than automatically defaulting to an overly conservative setting.
*Deco theory is just theory and your need for conservatism should be driven by your own particular body. If you feel overly fatigued or achy after a dive or series of dives, increase the conservatism a notch on the next diving day. If you then feel better after the next series of dives, make that the most liberal setting you use.
One cautionary note regarding you and your sig other's computers. Your more liberal computer is obviously putting hers into deco mode if it is requiring an additional 4 minutes beyond a normal 3 to 5 minute safety stop. I'd suggest three things:
1. Increase the conservatism of your computer. You can force any nitrox computer to act more conservative even if it is non adjustable by setting a lower nitrox mix than the one you are actually using one, you just have to be aware that any mod warning will be innaccurate so you have to know the shallower MOD of the mix you are really using.
2. If you tend to have longer bottom times, be sure to gear up early and be the first couple off the boat, then with the longer bottom time, you may be the last couple back on the boat, but you will be right behind the other divers and will not be holding up the show. Being slow getting off the boat and then going long on the bottom time is both inconsiderate and annoying to others and as you found out, potentially dangerous.
3. If you do deco dives, get training in deco procedures and configure accordingly with the required level of redundancy and gas planning. Also consider an advanced nitrox course and using a slung 30 or 40 with 50%, 80% or 100% 02 for a deco gas along with tables or a two or three gas computer like the Nitek Duo/Tusa IQ-700. It will get you out of the water cleaner and much faster.