The idea behind slowing/timing down/out is to allow the other tables to bust out before your table. When it get close to around 50 player before the bubble is usually when you should start evaluating.
How many BB do I have?
Should I tighten up and time out to let other tables play more
hands?
Is my stack headed for the final table?
A1: I have less than 10BB I need to find spots to shove
A1: I have 30BB i can play safe
A1: I have over 50 BB I can look to bully some medium stacks and steal easy blinds
A2: I need to find spots to get more chips because I have a small stack
A2: I can slow down the clock because I have a good stack
A2: I have a huge stack! Lets ( again ) bully and put pressure on others before the button
A3: I dont have a chance for the final table unless I get lucky.
A3: I can still look for spots to double up and get a nice stack headed for the final table
A3: I am set for the final table, lets start looking to knock people out!
These are just some examples of what goes on in my mind when I am close to the bubble. I have been in all three positions; short stack, medium, and big.
hope this helps