Around 4 days.
Our timeline: Approved 28th April, Sent to department of state 4th May, Welcome email 8th May. Both fees were attempted to be paid on 8th May, but DS-260 fees failed, re-sent 11th May. All final documents submitted 31st May (I had to wait for my police check as I wasn't ready for such a fast approval.) NVC RFE 14th June, RFE uploaded same day, DQ 15th June (Which also surprised me as I expected to wait 2 weeks again.)
I'm London embassy: IL received 29th June. Medical 13th July, Interview is tomorrow, 8th August.