L1 to L2..When is last day to work ?

[mfc]

While COS is being filing from L1 to L2, when should one stop working on L1 ?
Is it on the day of filing ? or on the day of approval ?

To apply for EAD on L2 for this case, is it possible to do in paralllel?
What documents are needed ? Is the receipt of COS is enough ?
Any replies highly appreciated.
Thanks in advance,
mfc