Hi
From how I understand it, when you use the Timer() to seed the random number the timer() part only starts when your app starts hence you get the same results, the easy way to use it is to have the user tap the screen to start the game then seed the random number as this at least creates a slight difference in the seed number as the player will not always tap the screen at the same time.
That is the easiest way I've found but like you say system time would be better if it existed.
Hope this helps some.
Scotty