Do I need to serve 90 day notice?

Do I need to serve 90 day notice to tenants after buying foreclosed multi-unit or is that just the time I need to wait before serving 3 days to quit notice? (JC in Los Angeles).

Under the Protecting Tenants in Foreclsosure Act you would need to give the tenants a 90 day notice or honor the terms of the lease. The laws may differ on multi unit residential properties so you may want to consult with an attorney in your area before you proceed.