curtain-up 
noun [in singular]
The beginning of a stage performance: curtain-up is at 8 p.m....
- The panto will be staged at Castlecomer Community Centre, with curtain-up nightly at 8 p.m. There will be matinee performances on both Sunday afternoons, for the children.
- At curtain-up, a chorus of Beefeaters and RAF chicks welcomes the royal family onto the stage, with each Windsor dressed in suitable garb.
- I can personally attest to the similarities between the atmospheres backstage before curtain-up and that of a restaurant in the buildup to a dinner service.