Time is running out for Elon Musk and his electric car company, Tesla. The serial entrepreneur promised investors that Tesla would be making 5,000 Model 3s per week by the end of June, and now all eyes are on Musk.

But it's not looking good.

This week, Tesla appeared to be behind schedule, despite the company's running two 12-hour shifts per day to make the vehicles, assembly line workers told  Reuters. A Monday shift produced 210 Model 3s, while a Wednesday shift produced 305 of the vehicles, the workers said. Tesla would need to average closer to 360 cars per shift to hit Musk's weekly goal. All of the company's factory workers have been instructed to come to work on Saturday, June 30.

"Basically, we have been in a long endurance race, and now the coach is yelling at us for a four-mile finishing kick," one employee at Tesla's Gigafactory near Reno, Nevada, told Reuters.

Musk first promised Tesla would roll out 5,000 Model 3s per week before the end of 2017, but in the last week of the year, the company made just 800. He later revised his target down to 2,500 per week by the end of the first quarter of 2018, but Tesla built only 2,020 during the final week.

Meeting these targets isn't just about fulfilling a promise. Musk needs to reach his production goals to keep Tesla profitable, something it has achieved in only two quarters since going public eight years ago. Tesla was burning through about $1 billion per quarter last year and ended 2017 with about $3.4 billion in cash, The Wall Street Journal reported. The company will continue to burn through the same amount until it reaches its goal of 5,000 cars per week, which would generate about $1 billion in capital in the short term. 

As investors and customers wait for updates, Musk says he's slept on the factory floor and spent his birthday working.