This is probably a cyclic discussion. Yet, I think it might be interesting, since the duel activity is not bad lately, and for sure there is people who could benefit from the help of others.

The questions for you are:
1) What items do you time...
1.1) ... when in map control?
1.2) ... when out of map control?
2) Timing Math? What's your mental scheme?
3) Timing statistics. How do you predict the spawn time when you're off timing?
4) Timing delays. When, how, why?
5) What do you think is the hardest thing related to timing?

You will get a [+] for elaborated answers!