You need to create a new field that tells you the length. We'll use the Len() function to return the length.
In a blank field in the query grid put this:
Length: Len([MyField])
Replace MyField with the name of the field you want to check the length of.
Set this new field's criteria to: >2
Or, for completeness:
Length: Len(Trim([Myfield]))
An NZ function in there, also, may not go amiss.