i want to talk mostly about quality assurance and change management in this post. writing english takes me a lot of energy so i try to make it short:-) First of all, i have no experience in open source projects and its change/release management methods, but i know how big banks and payment processors develop financial software. Also i do not know anything about the deployment process and policy of monero testnet.
new branch means new risk. to be on the safe side and flexible enough with this kind of branching i would recommend you having at least one more testnet instance. also i do not know how far you can run the trunk/your own branch locally, so its difficult to give an advice without really knowing how you prefer to work.
as long as open bugs still can be fixed, one month freeze sounds fine, maybe a little long, but depends on the testing efficiency too.
you devs know best if 6 months is enough or if 3 would be better (and off after 6), there is no need to punish yourself with this. as long as emergency changes are excluded of course (should be possible to completely disable this feature and hardfork immediately) me personally would welcome 3 months, but i do not know if this is possible with still keeping quality high and risks low.
in general i would not make to many rules so in the end you have to make a lot of exceptions. as light as possible is best.
my feeling is that 1 year is too long for now, but if we mature more it will be very useful for users to have this. (as we know allready, usability is key). even more non functional things like reliability and robustness of the network profit from it.
maybe you should also think about a method to estimate how much nodes/blocks allready use the new branch, so you can lower the praying even more once the real hard fork kicks in.
all in all, i like it. if i have more info i can give better advise regarding quality assurance