How to Execute Function to see the result in SQL

declare @aaa varchar(50)
select @aaa= dbo.Udfgetstarttimefromorderadvancedschedule(904977, '2018-02-25 00:00:00.000')
select @aaa

Go

select dbo.Udfgetstarttimefromorderadvancedschedule(904977, '2018-02-25 00:00:00.000')