Shiva Purana
पुनर्द्वितीये यामे च संकल्पं सुसमा चरेत् ॥ अथवैकदैव संकल्प्य कुर्यात्पूजां तथाविधाम् ॥ ६०॥
Then in the second 3-hour period Saṃkalpa rites shall be performed duly as before. Or the Saṃkalpa rite shall be performed once for all the four 3-hour periods. Worship shall be performed as before,
english translation
punardvitIye yAme ca saMkalpaM susamA caret ॥ athavaikadaiva saMkalpya kuryAtpUjAM tathAvidhAm ॥ 60॥
hk transliteration by Sanscript