Question about H1B transfers with multiple employers


I recently filed for an H1B transfer from company X to company Y. I started working 2 days ago for company Y, with the H1B transfer receipt. Now, I have another offer from company Z (which I prefer). Is there a minimum duration that I should work for company Y before I can jump to company Z with the company Z H1B transfer receipt. 

Also, since I have worked for 2 days at company Y, should I submit my I-797C (H1B Transfer Receipt) and my paystub from company Y? Would it be a transfer from company X to Z or Y to Z?

Please advise. I need to make sure before I make any hasty decisions. Thanks a lot in advance.

There is no minimum duration. You can start working immediately, even before you work for Company Y.

You should ideally submit the receipt from Y. Paystub - you can ask your attorney.