It won't work, as you could have determined by experimentation faster than posting.
Effectively, you are passing "constant path.xls" + curtme.
You need something like "constant path" + "separator char" + curtme + ".xls"
Separator char is in case you think this is not pretty enough
/home/stp/Desktop/STPAutomationFramework/ExportFiles/STPTestResults2015-03-15 13:33:16.xls'
and prefer something like
/home/stp/Desktop/STPAutomationFramework/ExportFiles/STPTestResults-2015-03-15 13:33:16.xls'
Note that curtime evaluates to something like '2015-03-15 13:33:16' and as you have avoided spaces everywhere else in the path, you may want to put something, e.g. "T" between the date and the time.
BTW your problem all about generating paths on the fly, nothing to do with excel.
BTW2 If you want your app to be portable: Windows won't like the colon (":"), and a whole lot of other characters.
HTH,
John