This is basically the system I used to use for rolling wilderness encounters back in the day, but I've updated it a bit. It assumes the DM is going to check the chance of an encounter based on the passage of time, not based on distance traveled. That's how it is in the dungeon, and that's how I've always preferred to do it.
Columns
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.
Rows
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.

Dawn

Morning

Afternoon

Twilight

Evening

Night

Plains

2d69

2d610

2d610

2d69

2d610

2d610

Forest

2d610

2d69

2d610

2d68

2d69

2d68

Desert

2d610

2d611



2d611

2d610

2d69

Etc.







2d69 gives the following percentages:
0: 83.3%
1: 8.33%
2: 5.56%
3: 2.78%
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 2d610, this chance is the same as rolling a 1 on a d12. For 2d611, 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 nonencounter 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 2d69 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 2d611 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.