This is an interesting Norwegianism (although it seems to occur in Swedish too - plenty of hits for ‘inte många minuterna’). It seems to mean exactly the same as ‘ikke mange minutter’ but it’s a bit more ‘folkelig’ (whatever that is in English!). It's used a lot with expressions of time (ikke mange dagene til jul) but can be used with various other nouns too. But it’s a bit mysterious why it seems to be ok with some nouns, but a bit strange, or impossible with others. ‘Det var ikke mange bøkene hun hadde i hylla’ or ‘jeg hadde ikke mange vennene da jeg var liten’ sound ok to me, but (after a visit to the dentist) ‘hun hadde ikke mange hullene’ or (after a birthday party) ‘det kom ikke så mange barna’ sound stranger (to me). No doubt if I thought a bit more, I could come up with some nouns which are quite impossible in the definite form after ‘ikke mange’, but I’ll leave it there and wait to see what other people think about this kind of expression.