Database
[{"startTime":1},{"startTime":2},{"startTime":15},{"startTime":23},{"startTime":0},{"startTime":0},{"startTime":2},{"startTime":251},{"startTime":52},{"startTime":12}]
Query
db.collection.aggregate([{$addFields:{tmpField:{$cond:[{$eq:[0,"$startTime"]},1000000000,"$startTime"]}}},{$sort:{tmpField:1}},{$project:{tmpField:0}}])