Update document field based on the current time

help
1

I need to update a field in a document, based on the current time.
For example, I have a document like this

{
 name: "Coffee market",
 schedule: {
  open: "1500",
  close: "2300"
 }
}

I want to have a field OpenNow that is updated reactively based on the current time, how can I do this?