This is an alternative time tracking system for your D&D 5th Edition games. The time slices are an easy way to keep track of the passing of time, without getting into the nit-grit of precisely knowing what time of the day it is.
For those who enjoying tallying stuff up, I provide also a resource tracking system that ties nicely with the time slices. It can be a bit computation-intensive, and it's only for those who like a more detailed tracking.
Each day is divided in 6 time slices, each one 4 hours long. In each one of these time slices the characters can "do stuff", typically adventuring, or researching lore, or crafting items, or partaking in some of the "downtime activities" described in the DM guides, or even just resting.
The time slices are as follows:
╔═════════╦═════════════════╗ ║ Hours ║ Slice ║ ╠═════════╬═════════════════╣ ║ 00 - 04 ║ Late night ║ ║ 04 - 08 ║ Early morning ║ ║ 08 - 12 ║ Late morning ║ ║ 12 - 16 ║ Early afternoon ║ ║ 16 - 20 ║ Late afternoon ║ ║ 20 - 24 ║ Early night ║ ╚═════════╩═════════════════╝
which maps nicely to the 24 hours.
A rough estimate tells that a medium-size dungeon, say 20 rooms, can be cleared in ~8 hours. Likewise, a small ruined town, say 15 buildings, can also be cleared in ~8 hours. This means that 2 time slices are required for clearing some standard elements of the D&D world.
The time slices make handling long rests easy: a non-elf character needs at least 2 consecutive time slices to gain the mechanical benefits of a long rest; elves need instead just 1, but it needs to be declared as a "long rest".
Short resting typically does not advance to the following time slice, unless the DM decides so, the rules are kept intentionally vague to avoid keeping track of the time, but in principle if the characters opt to take a short rest it's fine to leave them in the same time slice.
As a new mechanic, one can introduce the "medium rest": it takes the full time slice, it works as a normal short rest, but the healed hit dice are MAXIMIZED.
In principle, characters can forgo sleeping if they choose so. After a long rest, a character can stay awake without issues for a number of time slices equal to half their Con score. After that time, they need to make a Con ST each additional time slice they wish to stay awake, with a DC equal to the number of additional time slices (starting at 1).
If they beat the DC by 5 or more, they manage to stay awake without further issues; if they merely beat the DC, they stay awake but gain a level of exhaustion; if they fail, they succumb to sleep, and can't be woken up for a full time slice: when they wake up the Con ST is reset to 1, but they keep their exhaustion level.
A long rest resets the counter and, as usual, reduces exhaustion by 1 level.
A day of rations and two full waterskins contain sufficient food and water to sustain 4 time slices of adventuring activities, so we assume that each contain 4 food and 2 water units: a character needs to consume 1 food and 1 water unit for each time slice in which they perform some kind of intense activity. Resting does not count as an activity; however, after 4 consecutive time slices spent resting a character will still need to eat and drink 1 unit of food and water.
A character can go without food and water for a number of time slices equal to half their Con score, tracked separately. The same rules for the lack of sleep apply, with the DC for lack of food being 5 + additional time slices, and that for water being 10 + additional time slices. One difference is that lacking food or water can bring the number of exhaustion levels at 6: you can die of starvation or dehydration.
The Con ST for lack of sleep, food and water are tracked separately, and if a character is not fulfilling any number of these needs they roll separately for each.
╔═══════╦════════════════════════════╦═════════════════════════╦═════════════════╗ ║ Need ║ Intake ║ DC ║ Max exhaustion ║ ╠═══════╬════════════════════════════╬═════════════════════════╬═════════════════╣ ║ Sleep ║ 1 LR every half Con score ║ # of extra slices ║ 5 ║ ║ Food ║ 1 unit per "active" slice ║ 5 + # of extra slices ║ 6 (death) ║ ║ Water ║ 1 unit per "active" slice ║ 10 + # extra of slices ║ 6 (death) ║ ╚═══════╩════════════════════════════╩═════════════════════════╩═════════════════╝
A character succeeding on the "Foraging" action as described in the Dungeon Master's Guide procures 1d6 + Wis units of food and water if the DC is 15 or higher; and 1d6 + Wis units of food, and as many units of water the party is able to carry if the DC is 10 (it's assumed they find a river or a stream).
The spell 'goodberry' fulfills the food and water needs for 6 time slices.