Maribel and her daughter Jessie (Kecia Lewis and Antoinette Crowe-Legacy), in quarantine thousands of miles apart, first gossip about “Downton Abbey” —  how Lady Mary had sex with a diplomat who drops dead and has to figure out what to do with the body — before getting around to their own, admittedly more modest dilemmas — Jessie’s abruptly curtailed love life, Maribel’s agoraphobia —  in “When,” a charming and touching 20-minute play  by C.A. Johnson (best-known for her  “All The Natalie Portmans.)  “When” is the latest weekly offering of MCC Theaters LiveLab One Acts online. Directed by Taylor Reynolds, it is available for viewing through June 27.