Another easy way is formating as woooee just stated.
Here format so that your data show on line by line. So lets say you have the whole time stuff on line 5.
You just replace all line 5 with your new time stamp. Always think about future and updates. Planing is very important in programming.
Your case is solved. ;)
I have studied this very carefuly, that if a programe is well planed. Its very easy to update. No need for regex and crude methods. Regex in when all simple logic can not fix or you need need to find mixed up scatered data in a file.
Thats my take ;)