One of the most important tools in Time Management is Estimation. Read about it here.
it is important that you develop, early in the school year, a reasonably precise idea of how long it takes you to do things: for example, to mark a class of KS3 homework, or to write a quiz for a GCSE class.
Obviously, this estimate will not be accurate, but you must have some basis for routine planning - a rough idea of how long things take.
Note that TM4T demands a reasonably 'precise' idea of how long things take, not a reasonably 'accurate' idea. Your estimates will become more accurate in time, but it is valuable if you start with a precise estimate eg 4 ½ minutes not a vague estimate eg 'about five minutes'