I got these 74 min cd´s, CloneCd says they can store up to 79 min. Is CloneCd right? Can i really burn up to 79 min of music?

probably yes
I have gpt cdrw
it says that they are 74 min
but its 80 min

Data CDs require far more error detection/correction code than do digital audio and thus data CDs contain less useable ‘information’ to conform with sector sizes. The coloured books describe the standards (for the sectors) for each type of CD. If you’re interested, read here, here and here for more info.