For vertical grouting, the vents are placed ahead of time (during duct placement). Approximately 3-foot between outlet of the first stage and inlet of the second stage is a practical distance to allow for shut off. The grout would be setup and hardened between stages.
If you are not replacing a port or inlet before grouting you wait for the grout to harden. We would not recommend tapping a tendon that has fresh grout in it as it may create a bigger issue by bleeding down the liquid grout. This then would require further drilling and investigation. With the vacuum injection we can effectively fill voids most voids with hardened grout in the tendon.