On your second page that returns 01-01-1970, what does $oDate and $oTime contain? I would guess there is a problem with your form (or how you are reading the values from it).
You seem to be doing an excessive amount of (unnecessary) converting. Your first statement does the same as your second statement if you converted to "Y-m-d" format to begin with. What is preventing you from doing this in 1 statement?
The **reason** you get 01-01-1970 is that this is the beginning of the "Unix epoch" and you will always get this result if an invalid date is passed to most date functions - money's on penders' assessment. :-) Skip all that and use from_unixtime().