Question about Closing Date

Hi. Our purchase contract for a condo sets a closing date "on or about Sept. 30th." We as buyers would like to close as soon as possible, and not later than Sept. 30th. (Our financing is in place.) However, the sellers are taking their time getting out of their apartment, and thus, seem to be intent on extending the closing date. Our lawyer has told us that the "on or about" terminology has historically allowed a 30-day grace period. Does anyone have any experience with this aspect of closing? Is this 30-day grace period still applicable in the current market? Thanks.