Time Taken to L2 I94 Extension Receipt Number

My spouse and kids are on L2 visa, their I94 is getting expired before my I94 would expire. hence my company filed a extension petition for all my dependents. its been almost 1 and half months now, but till now I did not receive the receipt number. can someone confirm approximately how much time it takes to get the receipt number. after we receive the receipt number and before the petition is approved if the I94 expires, can the candidate stay in US on legal status.