I like to make quite large quantities of this and keep it in sealed, sterilised jars in the fridge, or give it as gifts at Christmas. If you want to make less, reduce the cooking time by 15 minutes or so.
Using condensed milk is only a partial cheat. It takes about seven hours to make doce de leite from scratch by slowly reducing and caramelising whole milk and sugar, but making it with condensed milk (which is just milk already cooked down with sugar) means you can skip the first five hours or so, and all the traditional stirring.
Don’t be tempted to make it by boiling sealed tins in a pan or pressure cooker. I saw the disastrous results of that technique going wrong in the first restaurant I worked in – fortunately, no one was hurt, but the prep kitchen was showered in boiling caramel.