The phrase "sign time" can pertain to a variety of concepts such as a signal to start, a period to signal the end, or an indication of when to do something. If you are looking for synonyms for this phrase, you can go for alternatives such as "cue," "indicator," "prompt," or "reminder." Other possible synonyms you can use are "moment," "interval," "momentum," or "timeframe." In contrast with these, you can also use phrases that pertain to the duration of a specific action, such as "duration," "pace," or "tempos." Regardless of the choice of word that you use, make sure that your chosen synonym is appropriate for the context.