The code given:

FE - D3 - DA - DA - D9

its possible to skip this next step, but it helps when you decrypt it. So I will convert this hex to binary:

11111110 11010011 11011010 11011010 11011001

Now I basically told you this was XOR encrypted, but I didnt tell you the key. However, I said " to look a little deeper it could take quite a large length of time"

This is tricky, but I was giving you a hint. The key is the length which is 101. Or 5.

Decrypted Binary:

01001000 01100101 01101100 01101100 0110111

Or Hello.

Now it was pretty easy to guess this one just by looking at the hex code. But its important to understand that more complicated clues and tricky codes could be given.