No, you can't take it immediately. Click on Schedule with Perason Vue in below page
https://learn.microsoft.com/en-us/learn/certifications/exams/ms-900
and it should give you 2 options - first is at test center and another one is online at your desk. You can try to schedule it on next day as you would need some time to set up things at your desk and also exam setup
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Please don't forget to Accept Answer and Up-vote if the response helped -- Vaibhav