Weeks of heavy rain have delayed the 12-week earthworks package at the site being carried out by Bam Nuttall.
The site preparation contract has now been extended by another four weeks to make up the time.
The local council stressed the extension would not delay main construction work on the £355m plant this summer.
A Staffordshire County Council spokesman told the Shropshire Star: “Following the wettest April on record, our contractors have had to extend working hours on site for a four-week period.
“This has no bearing on Jaguar Land Rover moving on site in the summer.”
Daily working hours have also been extended and the groundworks are due to be completed in July.
Interserve is understood to have won the main contract at the i54 business park from rivals Bowmer & Kirkland and Vinci Construction.