You can keep homemade guacamole in the fridge for up to 2 days. 3 in most cases will be absolutely fine. The key is to stop air getting to it so it browns. There are two ways you can tackle this. Pack the guacamole tightly into a bowl (press it down well with the back of a spoon) and then cover with clingfilm and press the film so it's actually touching the surface of the guacamole.