Regular expressions with dates and multiple matches

Question

I am currently attempting to automate modifying start and end dates within a .config file via powershell but I am having issues identifying the regular expression for the end date section since both are on the same line in the file. Below is the string that
I want to change.
Sometimes the dates are blank and sometimes the dates are filled in.
Dates are always in the same format (yyyy-MM-dd hh:mm).
I also want to note that there are multiple instances of 'StartDate="" EndDate=""' for other applications throughout the same config file so I cannot limit the expression to not include the App name. 
I do not want to limit the search to a line number since there are instances where admins will add an extra space in the config file that may throw off the line number.
I want to replace the dates or lack there of in their respective spots on the line below via powershell:
 <App name="TestApp" StartDate="2012-03-22 13:30" EndDate="">
I am successfully able to use 
$startRegex = '(?<=<App name="TestApp" StartDate=")([^"]*)'
to replace the StartDate but I can't seem to single out the EndDate with regular expression. What expression can I use to have it ignore what is in the quotations after StartDate and only pay attention to the EndDate value?
Below is a snippet: 
$path = d:\inetpub\website\app.config
$startRegex = '(?<=<App name="TestApp" StartDate=")([^"]*)'
$starttime = (get-date).ToString("yyyy-MM-dd hh:mm")
(gc $path) -replace $startregex, $starttime | set-content $path
I want to accomplish the same for EndDate.
Thanks in advance!

Answer 1

If you do this with XML it will be painless and less prone to error.
$n=$xml.SelectSingleNode('//App[@name="TestApp"]')
$n.StartDate=$newstartdate
$n.EndDate=$newenddate
$xml.Save($filename)
\_(ツ)_/