The reason to plant in autumn is to get that root network established. The reason not to plant too early is so that not too much of the stored energy from the bulb is used up growing tops that won't go to building the heads of garlic you want. Garlic is very hardy, and over the years I've seen very little damage to the plants because of cold weather. The tips may go yellow with the frost but the bulb should be fine.
One more tip is when you have mulched it, drop a bit of net over it because as winter approaches the pigeons will have less food available and your fresh green tips will look very appetising.
Last December I did a little experiment and planted 2 cloves in a 9" plant pot and stood it in the polytunnel. At the same time I put about 30 cloves outside.
The ones in the tunnel grew rapidly and I ended up with great long shoots that went into salads .. the bulbs were tiny.
The ones that went into the ground and had no protection at all, sprouted shoots just like yours and ended up like tennis balls. I now have enough hanging in a net to see me through until next year, plus I have a supply to plant shortly, that I know grow well in my soil.. make sure you do a few extras for growing purposes.