A few days back, Doug posted a column on his blog about time scale in games.
Violent Resolution - Time after Time
In it he mentioned the 5-second turns he used for our GURPS Alien Menace game.
In that game, they worked pretty well. Given the constraints of:
- online play
- multiple players
- PCs wanting contingent actions ("advance in overwatch until we see something")
- ranged combat
. . . it worked well. It allowed for us to more or less work as a group, fight as a unit, and otherwise blast anything that came into range. It felt realistic, too, which was important. Plus, it meant that most of the time there were steady and (for GURPS) long lulls between actual in-game actions.
It was a good call by Doug. Perhaps doing it another way would have worked as well, but the option chosen was effective.
This isn't the first time I've played with modified turn structure in GURPS. andi jones ran Gamma Terra with declared actions - go round the table, say what you'd do, then resolve them all in order. It made for a bit of a faster play pace, with overlapping actions that made sense when you decided on them but occasionally had odd results based on prior decisions by others.
I wouldn't use either outside of the genre we put them in, though. In a fantasy game, it might work, but equally, you have so many people crammed into tiny spaces slicing at each other with hand weapons most of the time. Fights are time-crunched grappling, split-second multi-foe kills, magically enhaced speedsters running around, area magic going off, strange special effects of all sorts. Either a longer time resolution or a declare-first approach would give more weirdness than verisimilitude and pacing.
In both cases, you can see where making a change to the resolution scale (or resolution mode) can shift the game's play for something that fits the specific situation.