Instead of using arbitrary units like hours or days, this system divides time into more natural sections based on sunrise, sunset, and the typical activity cycle of creatures outdoors. If your world has 2 suns or 60 hour days or other vastly different time schemes, just alter the column titles as appropriate, or add or remove whatever columns you need to make it work.
As far as the rows are concerned, you just need to have one for each encounter table (the thing that lists the actual monsters) that you've made.
"Aww jeeeez, this looks so complicated!" Bah, whinger! The idea is to make it as quick as possible while playing; to give the DM a rich answer to the question "does anything happen?" using as little dice rolling as possible. Then the DM rolls on their list of monsters/events/etc. for that area.
Result = No. of encounters for that period. Less than zero = zero.
2d6-9 gives the following percentages:
This means the overall chance of at least some kind of encounter is 16.67%, or the same as 1 in 6 on a d6. For 2d6-10, this chance is the same as rolling a 1 on a d12. For 2d6-11, this chance is 1 in 36.
When during the listed period does a rolled encounter occur? There are 2 main options:
1 - The DM rolls a single d6, with higher results indicating progressively further into the time period. If more than one encounter has the same result, they happen at roughly the same time.
2 - The DM decides how many hours are in each time period, then rolls randomly for hours and minutes. If the DM has a detailed calendar, the number of hours in each period may depend on the season.
The same 2d6 roll can be used to determine non-encounter events at the same time. If the roll on the above encounter table results in doubles, the DM would then roll on an event table. This allows for the chance of monster encounters to be different than the chance for events. For any area or situation, the DM can decide the chance of an event based on the desired probability below:
double 1: 2.8%
double 1 or 2: 5.6%
double 1 through 3: 8.3% or 1 in 12
double 1 through 4: 11% or 1 in 9
double 1 through 5: 13.8%
double 1 through 6: 16.7% or 1 in 6
As an example, if 2d6-9 is used for encounter chance, and an event is rolled on any double result, the overall chance of something happening is 1 in 3. Half would be encounters and half would be events. If instead 2d6-11 is used for encounter chance, and events are rolled on a result of either double ones or double twos, the overall chance of something happening is 1 in 12, with events being twice as likely as encounters.