The typical time a player will seek additional reflection time is when they believe they are faced with a complex situation (like a board with 10 creatures on each side). What both player and judge need to realize is that this situation is usually the result usually of a less complex situation last turn. Unless the game state has radically changed (such as Armageddon has resolved), complex situations arise over time and are not an excuse to play slowly.

the player still won't have moved in the following 10 or 20 seconds. This is the perfect moment to issue the infraction of Tournament Error — Slow Play. The penalty is a warning at all RELs.