Gavin Andresen said the best time to launch the block size increase update / hard fork would be the next reward halving (when mining discovery bounty would go from 25btc to 12.5btc). Why has halving anything to do with increasing odds of success of a hard fork?
Source: Gaving Andersen said that at the Dev Core conference London on April 19th in his keynote "Why we need a bigger chain". There was a live broadcast of the event but I can't find a video link.
A couple of months prior to a reward halving, the entire community is awake and excited about its prospects: this has happened not only with bitcoin but will the other alt-chains out there. So at this moment, bitcointalk, reddit, and most everyone is ready to listen and actually upgrade. At other moments, many people might "just be going on with their lives" and not following the news.
Technically, due to bitcoin's and other alt-coins successful reward-halvings, there are slim chances of major issues in the reward-half process. That codebase is extremely solid.
It's especially important that miners upgrade, or a hardfork will be created, with all the possible inconsistencies that could happen, drop in computational power, not to mention user confusion and trust in the network.
There's definitely no reason for that from a technical perspective. Success is entirely dependent on convincing all the wallets, nodes, and lastly miners in the network to make a breaking change to their software.
