§9.6. The time of day
Inform keeps track of the time of day automatically: play ordinarily begins at 9 AM and each turn takes one minute. In some works of interactive fiction, time of day is crucial: in others, it is irrelevant or even, by a sort of tacit convention, non-existent. So Inform does nothing to act upon the time, or to reveal it to the player, without instruction. Nevertheless it is there.
A sentence like the following allows the initial time to be set up as something other than 9 AM:
The time of day is 3:13 PM.
Here, "3:13 PM" is a constant value of a kind not seen before: it's a kind of value called "time", and the value "time of day" is a time that varies. After one turn it will be 3:14 PM, then 3:15 PM and so on.
Note that the sentence above is an assertion (a statement about the initial state of affairs), not an instruction which can be part of a rule. It would be equivalent to write:
When play begins: now the time of day is 3:13 PM.
We more often change "time of day" to take care of drastic events:
At the time when the player loses consciousness:
now the time of day is 10:12 AM;
say "A mist comes over your vision, and when you come to, it is morning and you are in bed."