Jose,
Thanks for your interest in NetLogo modeling! This forum is for talking about development of the NetLogo application and other software using its APIs. For general modeling questions, I recommend using the NetLogo Users group:
https://groups.google.com/forum/#!forum/netlogo-users
A tick is just a tick, it doesn't represent any particular length of time. It also doesn't take any definite real-world length of time to execute, it's just a counter that is usually (but not always) updated by the model after one "round" of updates for a model. Each model can then decide how long a tick is, depending on what's being simulated.
Good luck!
-Jeremy