The ticking clock is adding urgency to the negotiations of new contracts for the five key stars of “The Big Bang Theory,” with sources suggesting that the constituencies are bracing for a long working weekend in the hopes of getting deals in place by Sunday night.

There is speculation that the days lost this week after production was delayed from its scheduled July 30 start have already cost the Warner Bros. TV sitcom one episode from its 24-episode order for season eight. However, others close to the situation insist that five production days can be made up down the road to avoid trimming down to 23 episodes.

CBS is counting on airing back-to-back new episodes of “Big Bang” on Sept. 22 to give a boost to its new 9 p.m. drama “Scorpion.” “Big Bang” will move back to Monday nights temporarily this fall to make room for the addition of eight NFL games on CBS’ Thursday slate.

The talks between the studio and reps for the thesps — Jim Parsons, Johnny Galecki, Kaley Cuoco, Simon Helberg and Kunal Nayyar — have been stepped up in the past few days. But sources close to the situation say the process has been slowed by the fact that the actors’ reps are negotiating separately and most are focused on achieving pay parity — which means that each is holding out to hear what the latest offer is for the others before committing to a three-season deal.

The money on the table for the actors is considerable — around $1 million an episode for Parsons, Galecki and Cuoco, plus a larger sliver of the backend — but so are the profits that “Big Bang” is generating in syndication. Helberg and Nayyar have to date earned lower fees than the other three and are said to be hoping to close the gap considerably in this negotiation. Sources said Parsons’ team has been aggressive in pushing for a higher salary given his high profile in pop culture and track record as a three-time Emmy winner who is up for a fourth trophy at the Aug. 25 Emmy ceremony.

Not surprisingly, there is plenty of finger-pointing as to why the sides were unable to reach a deal by the July 30 start of production. Knowledgable sources characterize the actors’ camps as having unrealistic expectations about the kind of money that can be feasibly paid to the actors. From the thesps’ perspective, it’s only fair that the stars share meaningfully in the off-network windfall.

Contract wrangles between talent and the studio on successful shows, particularly sitcoms, are nothing new in TV. But “Big Bang” has by all accounts been a mostly harmonious set, which makes the current tension all the more unusual for the players. As always, the biggest losers will be the show’s craft and crew members if the production delay drags on and scheduled lensing days are lost.

The hope is that the sides will hunker down and make enough progress during the weekend to allow for work to begin on Wednesday. Even if deals are in place by Sunday or Monday, it’s understood that the actors would not go back before Wednesday.