How to Add Instruments Partway Through a Score?

Background Info on Score:
Total Parts: 4 (SAB Voices + Piano)

To begin a song I am scoring, the soprano part begins singing one verse, and then the piano and other two vocal parts come in. Instead of having the Alto, Baritone, and Piano parts sit empty for ten measures, I'd like to start off with only the sopranos on the score and add the other two parts onto the sheet when the time comes for them to begin playing or singing, as the case may be. Basically, I'm wondering if you can set parameters for where an instrument starts and ends its appearance in the score.