I think the standard is every 2min on arrivals for DFW
in rush hour. My mom's first cousin was (may still be) the airport manager at Alliance in Fort Worth, Texas. He told me the 2min rule in 2000, things may have changed for departures after the AA587 crash on the Rockaways in Queens, New York in 2001.
The ATC working the tower at Alliance was transferred from DFW
because he had problems with spacing for takeoffs. Alliance had next-to-no traffic then, just WN
pilots practicing IFR landings after midnight.
Keep on truckin'...