Three months to fill it? If the tumbler is full and it's not decomposing, you might want to consider emptying it out. I'll assume that you've got an adequately reasonable carbon/nitrogen ratio. Since you have been turning the tumbler, it will be pretty well mixed. Dump it out and move the contents to a compost pile. Starting filling the tumbler again.

In three more months you will have filled the tumbler again. The weather will be warming up, the contents of the tumbler will be composting and shrinking down. Be sure to stop adding material so that it has a chance to finish before planting time. Once you've got that about halfway composted, you'll want to dump that compost into a pile, too, so it can finish. Don't mix the first pile and the second pile, but do turn them and keep them damp.

You can test your compost to see if it's ready by trying to sprout small seeds like carrot in the compost. Not ready? Turn it and keep it damp, but not wet.

Don't use unfinished compost on your soil. Once your plants have sprouted or are transplanted and established, you can top-dress with your new compost.

Cooler ambient temperatures will slow down the decompostition and if it gets cold enough (frozen), stop it completely. As long as it's not frozen, there will be something going on and at cooler air temperatures, frequent tumbling isn't necessary unless the 'post is hot. It's the creation of the heat that requires the increased oxygen. If it's slow and cool, it doesn't need as much air so it doesn't need frequent mixing.

At night, throw an old blanket or piece of carpet over the tumbler to restrict heat loss. This might also qualify you as a compost whacko enthusiast and people will look at you funny when you tell them you have to tuck your compost in for the night. BTDT.

Lloyd