TIER 2 EXTENSION CONFUSION PLEASE HELP

[golekipro]

Hi I am currently on Tier 2 visa which is expiring in March 2017. I am eligible for an extension. I have few basic questions:
1. when I should apply for the extension?
2. For how long extension will be granted?
3. Does making an application early will affect my 5 year eligibility for ILR?

Thanks in Advance for assistance

[iworker]

1. whenever, but before expiry date.
2. as per cos, but total tier 2 duration cant be more than 6 years.
3. as long as the duration makes 5 years, no.