How to get all IDs from Mongo with no record in the past hour

You can use $group aggregation to find the unique record for the imei field and use moment library to cut of the last hour from the current time.

db.collection.aggregate([
  { "$match": {
    "datestamp": {
      "$lte": moment().subtract(1, 'hours').toDate()
    }
  }},
  { "$group": {
    "_id": '$imei'
  }}
])

Or even you can use distinct query as well

const imeis = await db.collection.distinct('imei', { "datestamp": { "$lte": moment().subtract(1, 'hours').toDate() } })
console.log(imeis)