The phrase "time in" can refer to various activities and tasks such as clocking-in for work, logging in to a system, or starting a countdown. Depending on the context, there are different synonyms that can be used instead of "time in". For example, instead of "clocking-in", you could use "punching-in", "registering", or "signing-in". For logging in to a system, "accessing", "logging-on", or "entering" could be used instead. To describe starting a countdown, "commencing", "initiating", or "launching" could be used. By using different synonyms, it can add variety to your writing or communication while still conveying the intended meaning.