[{owner:"0x123124124",createdAt:"13 May 2022 at 04:20:21 UTC"},{owner:"0x123124124",createdAt:"13 May 2022 at 06:20:21 UTC"},{owner:"0x123124124",createdAt:"13 May 2022 at 03:20:21 UTC"},{owner:"0x123124124",createdAt:"12 May 2022 at 07:39:34 UTC"},{owner:"0x123124124",createdAt:"12 May 2022 at 07:39:34 UTC"},{owner:"0x454545627",createdAt:"11 May 2022 at 04:13:48 UTC"}]

db.collection.aggregate([{$set:{createdAt:{$trim:{input:{"$arrayElemAt":[{$split:["$createdAt","at"]},0]}}}}},{$group:{_id:{owner:"$owner",createdAt:"$createdAt"},count:{$sum:1}}},{$project:{_id:0,owner:"$_id.owner",createdAt:"$_id.createdAt",count:1}}])