By default the block time for nxt is 60 sec average this is question.
This parameter can be changed to a lower time 10 sec for e.g?
And if yes what would be the possible impacts (negative and positives)
Yes, the block time can be changed, but not very easy. There are two ways to do it:
A negative effect in both cases is that there will be less time for nodes to communicate new blocks and consequently more spontaneous forks will appear. And the number of blocks will grow 6 times faster.