I agree this is one option. What it will tend to do is make strategic choices a focus of play. That can be good or bad, depending on what one is looking for from an RPG. For someone who finds the strategic and operational side of play somewhat dull, it may be better to have other approaches to the 15 min day - like reducing the importance of daily resources, or putting various de jure or de facto limits on the players' ability to access them.All that needs to happen is that players need to be aware that there are penalties for abusing the idea of the 15MAD.
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I think that one of the big psychological hurdles you have to overcome is a willingness to punish your players for poor strategic choices.
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Therefore as a DM I think it's important to have a vision of what 'good' play is and enforce that vision with real consequences for the players.
Different approaches for different playstyles.
In my experience, this is not true. The 15 minute day can also work in a game in which the gameworld is responsive and not-static, but in which the focus of the PCs' attention (say, some ancient and uninhabited ruins, protected by magic that only high level spell casters - such as the PCs - can penetrate) is not likely to change much over the course of days and weeks.The 15MAD only works in campaigns where the game world is static, unchanging, and unresponsive.
My own world, which is the real world, is not particularly static, but it is equally true that few of my deadlines are so hard that a day here or there in the course of working towards them is going to matter. The same thing can often be true in an RPG (and [MENTION=22779]Hussar[/MENTION] makes this point well).
These sorts of cases have been discussed in another current thread on the Legacy forum.NPCs who will kill the hostages. NPCs who will pack up their stuff and go somewhere else if the PCs give them time to escape.
And again it is a playstyle thing. In my game, I would never have the NPCs kill the hostages offscreen in circumstances in which the players are committed to having their PCs rescue them. It would be too anticlimactic. If the hostages are going to die, it is going to be in circumstances where the PCs are about to rescue them, and fail.
In my experience this can produce a degree of frustration, if the players are continually committing resources that they rarely need to call on.Get the spellcasters to hold back 20% of their spells "just in case" and invest another 20% of their spells in non-combat utility (that may or may not come in handy that day)
Again, I think this is a playstyle matter. The more that players enjoy the planning, operational and strategic side of play, the more they will enjoy this sort of "being clever" even if they never, or only rarely, get to cash in their cleverness. For those who find operational issues a distraction from the real game, I would look to other solutions for the 15 minute day - or, alternatively, I would embrace it as part of play (which I have certainly done in mid-to-high level Rolemaster games).