I think that's extremely short, even assuming there is no controversy about changing the rules at all. Things like BIP65 and BIP66 already took significantly longer than that, were uncontroversial, and only need miner adoption. Full node adoption is even slower.
BIP65 and BIP66 were uncontroversial, but also generally uninteresting. Most people don't care about OP_CLTV right now, and they won't for quite a while longer. They neglect to upgrade their full nodes because there has been no reason to.
Given that a supermajority of users and miners have been asking for a hard fork to increase the blocksize for years, I do not think that mobilizing people to upgrade their nodes is going to be hard.
When we do the hard fork, we will need to encourage people to upgrade their full nodes. We may want to request that miners not trigger the fork until some percentage of visible full nodes have upgraded.