Broadway previews began on Wednesday evening, November 2, 1966.
Some online sources give the number of previews as having been 21, but that is incorrect. The correct number of previews is 20. It would have been 21 had there been a performance on Thursday, November 17, but with a Sunday night opening later that week, there was no performance on the 17th.
In addition, some online sources give the date of the final performance at the Imperial as having been October 2, 1968, but it was October 5, 1968.