Is the short message notice of returning to work within a time limit valid in Beijing?

Effective. The unit requests to resume work and sends a notice of resumption of work, which has legal effect. Refuse to return to work without justifiable reasons, the unit can be regarded as absenteeism. The notice of resumption of work will take effect as soon as it is received, and there is no need to send it again. The notice is legally binding, but it depends on what it is aimed at. If the content of the notification letter includes things that have not been done, it should be unreliable and may have received false information about criminal incidents.