Time signs usually occur at the beginning of a sentence to establish tense. All the following events described are understood as occurring at the time.
If a time sign is not specified, then it is assumed that the events described are in the present tense.
Verbs in ASL are not modified specifically for tense like in some other languages. Hurrah!! No conjugated verbs!
Time Signs reflecting tense are on an imaginary timeline like this video below. Time signs referring to the future tend to move forward: Time signs referring to the past tend to move back, and time signs referring to the present are usually signed right in front of the body.
Please watch carefully how the signer demonstrates the basic sentence by using FINISH with the raised eyebrows