there is something tru about this its same with everything in co,like hunting,doin moonbox,socketing,geting 5x exp from x-mas quest,uping with mets and dbs.
sometimes i fail tons of mets on item doing it from lvl 52>67 (earring for the example) and then it pass and got it to 112 with 1 met per upgrade.but u know u should do it fast becouse that time is like 30 sec for example every 5 mins u have 30 sec period where u dont fail.So this hint is realy usefull but it cant always work for example u upgrade 82lvl item to 97 in 1 met then u open the warehouse get money,db,item then repair the item then put and upgrade and that 30 secs already passed and u fail,