请教大家， 从网站看到：http://www.h1base.com/visa/work/H1B%20Visa%20Transfer%20To%
20A%20New%20Employer/ref/1169/ :
Current H1B visa holders can change and start work for a new employer as
soon as an H1B transfer petition is 'submitted' to the USCIS by the new
employer.
问题： 我目前在公司A工作(H1B)，如果公司B给了我OFFER，我什么时候能到公司B工
作：
1。公司B将H1B Transfer 的申请文件上交到移民局的那天？
2。要等到转H1B被批准的那天？
如果是1的话，万一移民局没有批准我的H1B Transfer怎么办？
The H1B transfer bill approved in the senate and House (bill S.2045) now
enables valid H1B visa holders to change jobs upon the filing of a new petition
by the new employer as long as the individual is in lawful status at the
time of filing and has not engaged in any unauthorized employment since
his or her last lawful admission.
Allows individuals who have filed for adjustment of status and whose cases
have been pending for 180 days or more to change jobs or employers without
affecting the validity of the I-140 or underlying labor certification, as
long as the new job is in the same or a similar occupational classification
to the job in the original petition and labor cert.
问题： 那个180天是什么意思？
THANKS A LOT.