Is it okay to wait 30days to join Deloitte USI as immediate joiner

I do have an offer in hand with some company doj as 18th aug And I got offer with Deloitte USI I'm an immediate joiner But they said they will take 30days time before onboarding a candidate for bgv. Is it okay to wait for 30days to join Deloitte USI Will there be any risk in waiting Does they put onboarding on hold or revoke or anything risky