Any person who prior to March 4, 1915, made homestead entry under the Act of June 17, 1902 (32 Stat. 388), for land believed to be susceptible of irrigation which at the time of said entry was withdrawn for any contemplated irrigation project, may relinquish the same, provided that it has since been determined that the land embraced in such entry or all thereof in excess of twenty acres is not or will not be irrigable under the project, and in lieu thereof may select and make entry for any farm unit included within such irrigation project as finally established, notwithstanding the provisions of sections 436 and 437 of this title: Provided, That such entrymen shall be given credit on the new entry for the time of bona fide residence maintained on the original entry.