Do you add "在“ before saying "___年“？ I'm trying to remember what is the proper way to use time. Do we ever add 在 before a year when writing? Or do we generally not add it? Here's an example sentence that I wrote. Would you add 在？ 


  在2006年， 当刘强东正在寻求资金时， 中国的物流系统非常糟糕。
You sentence is correct with or without the 在. Using 在 will put a bit more emphasis on the year, while leaving off 在 will put a bit more emphasis on the action. Also, if you're listing years, you would not use 在:

2006年，中国的物流系统非常糟糕。2008年，仍然糟糕