The CFR does not specify how quickly Level I's must be completed, and with good reason: There is no baseline against which to establish timing requirements.
A PASRR Level I screen must be completed for all applicants to a Medicaid-certified nursing facility, regardless of payer. A Level I screen must be completed before a resident can be admitted into a nursing facility.
For a variety of reasons, including the availability of evaluators, it may not always be possible to perform a complete psychiatric evaluation on an individual before they are admitted to a NF.
42 CFR 483.130(o) has this to say about the retention of PASRR records:
A level II Preadmission Screen (PAS) must be completed for all applicants who meet NF level-of-care requirements, and who have been identified as having possible MI and/or ID by the Level I evaluation.