Musk tells remaining Twitter employees to sign up to "high intensity and long hours" or resign - and says they must be "extremely hardcore".
has said he plans to reduce his time at Twitter and eventually find someone else to run the company.
Musk made the remarks while testifying in the US state of Delaware, where he's defending himself against claims from shareholders that his $56bn (£47bn) pay package at Tesla
was too generous.
"There's an initial burst of activity needed post-acquisition to reorganise the company," Musk said in his testimony.
"I expect to reduce my time at Twitter and find somebody else to run Twitter over time," he added.
He also revealed he hoped to complete the restructuring of the organisation this week in a bid to ease the turbulence that has reigned since his takeover.
Rapid change has occurred at the company since Musk's acquisition, including a gutting of senior management and laying off half the workforce.
In further moves to shake up the firm, Musk has sent a message to staff warning them of a coming change in culture.
He told them them they had until Thursday to decide if they wanted to stay on at the company to work "long hours at high intensity" or take a severance package of three months' pay.
Musk told Twitter employees that anyone who had not clicked on a link confirming "you want to be part of the new Twitter" by Thursday evening New York time would be considered to have quit.
"Going forward, to build a breakthrough Twitter 2.0 and succeed in an increasingly competitive world, we will need to be extremely hardcore," the message said.
"This will mean long hours at high intensity. Only exceptional performance will constitute a passing grade."
Musk said Twitter would be "much more engineering-driven" under his leadership, adding that "those writing great code will constitute the majority of our team and have the greatest sway."
The billionaire has also abolished remote working, saying staff would be expected to be in the office at least 40 hours per week and warning Twitter might not "survive the upcoming economic downturn".
He has also taken a no-nonsense approach towards employees who publicly criticise the company.
Several former staffers suspect they have been let go for posting critical comments about Musk or the company online.
One source told Reuters he received a termination email overnight that said "your recent behaviour has violated company policy", and said he believed over 20 people were fired in the latest round.
Several others tweeted on Tuesday that they had received the same emails.
"I would like to apologize for firing these geniuses," Musk tweeted on Tuesday. "Their immense talent will no doubt be of great use elsewhere."