Start date of Blanket L1 petition

[Undead]

Hi all,

I am trying to schedule my L1B visa appointment at the Chennai Consulate. It is based on a blanket petition. The traveldocs.in site asks for the petition number, start date and expiry date. What should I write as the start date? It it the 'valid from' date of the blanket petition or my expected employment start date?

Thanks.