Dat kan in 2 stappen:
var objIdMin = ObjectId(Math.floor((new Date('1990/10/10'))/1000).toString(16) + "000
0000000000000")
var objIdMax = ObjectId(Math.floor((new Date('2011/10/22'))/1000).toString(16) + "000
0000000000000")
db.myCollection.find({_id:{$gt: objIdMin, $lt: objIdMax}})
of in één stap (wat minder leesbaar is):
db.myCollection.find({_id:{$gt: ObjectId(Math.floor((new Date('1990/10/10'))/1000).toString(16) + "000
0000000000000"), $lt: ObjectId(Math.floor((new Date('2011/10/10'))/1000).toString(16) + "000
0000000000000")}})