Tier 2 Switching the employer and 5 year CoS

[Merry]

Hi,

I got my Tier 2 visa on July 2013 and now would like to switch the employer. I already used up my 1 year 7 months from my 6 year total Tier 2.

So now my question is can I apply for a Tier 2 visa of 4 years 5 months together under the CoS category 5 year Or is that category is only for candidates who can apply 5 year at first time itself. One of my solicitor friend told me I can apply for only 3 year Cos , is that right?

2. After getting the visa under new CoS if my start date is 1 month ahead can I do my notice period - 1 month, is that legal?

Many thanks in advance.