I cut my clones a couple of nodes longer than usual, seal them into freezer bags, stick them in a plastic lunch box, bag the box and write the date on top, stick it in the crisper draw (7C) for up to 8 weeks. Personally, I haven't gone further than 8 weeks.

When it's time for cloning I let the lunch box acclimatise to room temperature before opening, mist the foliage, recut the stems, and then it's the same process as cutting fresh material.

Takes a few days longer to root and a few days longer to acclimatise to lower humidity, but it's a mighty useful way of making sure you always have clone stock.