Custom Formula error returning a date

I am trying to create a custom formula field in Leads, but I am getting a syntax error. The formula Return Type is set to datetime:

If(${Leads.Outbound Stage} == 'SQL 020', now(), adddate(now(), 4, 'DAY'))

I get this error: Your string is either missing its quote marks, or it needs a comma separating it from another value.

The Leads.Outbound Stage field is a dropdown list of set options.

I ultimately want to create a date field that is changed based on the value of the Outbound Stage selection. A formula field feels right, but if there's another approach (aside from creating a separate workflow rule for every value) I'm open to it!

Thanks,