Now I understand what the Colregs say and I'm not interested in bashing them out again here (unless somebody can point me to a sub clause that answers my question).
My boating background was almost entirely made up of day trips of only a few hours (and night cruises in the swan, so doesn't really count), in a small yacht, other people's yachts or powerboats. Nice days, social and more then happy to be in the cockpit.
Since embarking on the the delivery of Mikado from Brisbane to Perth, we have now done a dozen or so overnight passages and a handful of multiday passages -Thursday Is to Gove, Darwin to Berkeley River and now 350nm Broome to Dampier. On all our passage making day or night, we have had somebody in the cockpit (not necessarily at the helm).
It is currently 8:30 in the morning and the sun is already belting hot. Stepped downstairs where the kids are playing cards and the missus is sleeping to make a brew and it was a much more comfortable environment.
So so there is nobody within cooee, and the closest AIS target is over 100nm away with a CPA of 75nm (I know, I know and we're not going there either) and 20nm off the coast. I don't see the difference and being emerged in a book, music, movie or whatever and looking up every 10 mins or being down stairs and popping your head out every ten mins. Especially of a night time when (in my cockpit at least) you are/feel rather exposed.
How much time time do you spend in the saloon when on watch?
We must be old fossils because on Trek someone must be on deck on watch 24/7 when underway.
Even when one boat I had had radar we could watch down below while it was freeeeezing upstairs someone was on deck on watch.
AIS is good but cant see a boat without it ... or a container and they dont have AIS 
always someone on deck except for toilet breaks probably why i dont like the idea of more than a day single handed
When singlehanding, 20 mins. Daytime is not so bad, but I must admit, at night I struggle lasting 20 mins though before being up in the cockpit looking around and doing all the checks, just too paranoid.
This means fatigue builds up and limits how far I can travel before anchoring up or heading for a marina. It also surprised me how much fatigue can impact your rational decision making.
I've been practising techniques on how to get decent sleep for those 20 mins and I have yet to really nail the knack of it, it's a work in progress.
In a busy area, or in land locked areas, different story of course.
A few diverse responses straight up. Thanks for the replies.
Just to clarify, I'm not talking about sleeping because there are two of us. There is always somebody awake and alert. I was just wondering where people spend the majority of their time whilst on watch.
Cheere again 
Out at sea at night happy to scan the horizon every 10 minutes or if solo 20 minutes will have ais on though
I'm with you Toph 15 to 20 min visual watches is all that's needed when offshore. I have been toying with the idea of fitting fore n aft 180 degree fish eye video cameras for day passage making.
A egg timer can also be handy to set each time you go below.
To the Whitsunday's and back, overnight two handed and day time single handed, none. Except, when single handed, I parked the boat for a comfort stop and coffee.
I may have a different answer when I have an autopilot.
We travel short handed with no AIS. Someone on deck at all times. We are only coasting but do travel overnight.
Cheers
Bristle
Coastal I stay in the cockpit mostly, going below to cook and make a brew. Just make a comfortable nest and get into a good book. Offshore I'll sleep below for an hour at a time.
All about the level of risk you're happy to accept.
Several recent post's about accuracy of charts and reliability of autopilot's add to that.
Also have to remember that there are plenty of things in the water that only let you know they're there by bumping.
Location plays a big part, what traffic happens there and nearby.
Are you confident that anything that is currently over the horizon won't surprise you in 20mins, taking in to account maybe a 20-30 knot closing speed.
I do all of that above in various forms, but just remember, if you see a boat below the horizon its BLOODY CLOSE!!!!
