[{_id:1,value:"25 hr 2 mins"},{_id:2,value:"25 hr 36 mins"},{_id:3,value:"25 hr"},{_id:4,value:"36 mins"}]

db.collection.aggregate([{$set:{value:{$regexFind:{input:"$value",regex:"(?:(\\d+) hr){0,1}\\s*(?:(\\d+) mins){0,1}"}}}},{$set:{value:{$round:[{$sum:[{$toInt:{$arrayElemAt:["$value.captures",0]}},{$divide:[{$toInt:{$arrayElemAt:["$value.captures",1]}},60]}]},2]}}}])