The blocktime for each chain is 10 min per block. If blocks are created too fast, the difficulty is adjusted.
there is no such thing as "blocktime" and "10 min per block". the only time related variable that we have is 2016 blocks in 2 weeks and that is what is checked to adjust the difficulty.
Given these limitations how is it possible to build an alternate chain that grows much faster than the honest chain?
you perform 51% attack by having >51% of hashrate!
in other words you should have more than half of the hashing power of the whole network so that you can find more blocks compared to the rest (the <49%), and that way you create the longest chain.
remember that 51% is the bare minimum, it is not possible to actually do it with 51%, you need a lot more than that to successfully pull that off.