What is first time travel period validity for a new H1-B?

My H1-B is valid till End 2015. But the present employer did not get me to US after H1-B approval. In this case, till when can I search a new job in US and Transfer my H-1B to new employer and travel to USA?

You can travel to US till you have 45 days H1-b validity left on your visa. But the companies generally send employees 60 days from expiry if they’ve not sent the employee till then.

For transferring to a new employer - I’m not sure but I think 2 payslips in the US are required.