I think Dave McCallum says a 5 second squeeze. If you over fill it, it will squish out the top, don't worry about overfilling.
I've never liked the "6 months" or the periodically type time references in the manual. If you use the machine every day all day, it's going to need service sooner than a machine I use once a month. Best thing to do is to listen and smell your machine. For things like grease that it will consume, top it off when you remember. If it squishes out the top, it's probably still full.
We do call it a FW tattoo for a reason.
I have a pair of them.