Database
[{_id:1,value:"25 hr 2 mins"},{_id:2,value:"25 hr 36 mins"}]
Query
db.collection.aggregate([{$set:{value:{$regexFind:{input:"$value",regex:"(\\d+) hr (\\d+) mins"}}}},{$set:{value:{$round:[{$sum:[{$toInt:{$arrayElemAt:["$value.captures",0]}},{$divide:[{$toInt:{$arrayElemAt:["$value.captures",1]}},60]}]},2]}}}])