I don't want them to all ripen at the same time, so I'm phasing the process: most of the batch went into the fridge so they could stay unripe longer, and then I wrapped the ones I wanted to use to ripen them.
I did a cursory search on Google just to see how other people ripen their avocados. There were a lot of posts about ripening an avocado in 10 minutes by putting it in an oven.
When they are in season, avocados are staple in our our meals: we use them instead of butter/margarine on bread, as part of sandwich fillings, salads and dips. I've never ripened them in an oven though, probably because when you grow your food, you get used to being patient and eating what's available when it's ready. Also, it's probably out of ignorance, but I'm a bit wary about whether using heat like that affects the quality of the fruit. So I decided to go with the process I'm used to:
Step 1: Line a basket with newspaper or cloth and then put the first layer of avocados in the basket.
Step 2: Cover your avocados with newspaper/cloth and then put in the second layer of avocados on top
Step 3: Cover the basket to make sure your avocados are in a warm, dark and cozy place.
Step 4: Put the basket in a cupboard (I usually put on a pantry shelf) until they are ready to use.
It usually takes 1-3 days for the avocados to ripen depending on their state when I received them (were they already in the process of ripening) and daily temperatures in my area at the time. So I check daily, take out the ones which are ready and leave the rest to continue the process.
The South African Avocado Growers Association also gives some advice on ripening and storing avocados.
They say: "To ripen avocados at home, keep them at room temperature until they are ripe. To accelerate the ripening process, place avocados in the fruit bowl with other fruit (especially bananas), or better still, pop them into a brown paper bag with the bananas."
I'll try that next time I have bananas and avocados at the same time.