TKOF BELOW REQUIRED MINIMUM VISIBILITY AT DEN; CO.

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MY COMPANY IS A PART 135 CARRIER FOR AN ACR. WX AT MY DEST WAS 5 MI BELOW MINIMUMS FOR DISPATCH. THE ACR SUPVR ON RAMP TOLD ME TO DISPATCH ANYWAY. I REFUSED AND REFILED X TIMES WITH FSS AND CHANGED MY DEST. MY COMPANY'S CHIEF PLT/DIRECTOR OF OPS ALSO TOLD ME TO DISPATCH. OBTAINED WX FOR DEST AND FILED. FELT EXTREME PRESSURE TO DISPATCH BY MY COMPANY AND BY THE ACR SUPVR. NEW DEST WAS ABOVE MINIMUMS AND OBTAINED CLRNC; PICKED UP ATIS INFO; VISIBILITY 10 MI 9000 FT 25000 SCATTERED. WHILE GETTING TAXI CLRNC; A FOG ROLLED IN ON CARGO RAMP AND SEVERELY LIMITED VISIBILITY. ON TAXI; THE TAXI ORDER WAS OUT OF SEQUENCE AND ACFT WERE TAXIING OUT OF ORDER. I TAXIED BEHIND 4 OTHER ACFT AT A VERY SLOW RATE. ON TAXI OUT; I RECHKED ATIS AND THERE WAS NO CHANGE. THE GND FREQ WAS EXTREMELY CONGESTED; AND ACFT KEPT STEPPING ON EACH OTHER SO UPDATED WX WAS NEVER XMITTED OVER RAMP CTL FREQ OR GND FREQ. I CHKED THE ATIS FOR THE THIRD TIME WITH NO UPDATE FROM INFO. I WAS CHANGED TO TWR FREQ WHERE ANOTHER FREIGHTER WAS ON DEP ROLL RWY 35L. I MISSED TWR'S RPT OF THE RVR. I WAS TOLD TO HOLD SHORT OF RWY 35L AT TXWY M2. I WAS UNABLE TO TAXI AROUND ANOTHER ACFT BLOCKING MY PATH. THERE WAS ANOTHER DEP RVR RPTED AT 1800 FT AT TOUCHDOWN; 1400 FT RVR ROLLOUT. THERE WAS A LNDG WITH SOME RVR VALUES RPTED. I WAS CLRED TO POS AND HOLD AND THEN CLRED FOR TKOF AFTER THE ACFT CALLED CLR OF THE RWY. ON MY DEP ROLL RVR WAS RPTED TO ACFT HOLDING AS 1400 FT RVR TOUCHDOWN AND 1400 FT RVR ROLLOUT WHICH IS BELOW THE REQUIRED 1800 RVR TOUCHDOWN RVR REQUIRED BY COMPANY'S OPS SPECS. CONTINUED TKOF WITHOUT INCIDENT. 3 FACTORS I FEEL THAT LED TO THIS UNINTENTIONAL EVENT: 1) PRESSURE FROM NOT ONLY MY COMPANY BUT CONTRACTEE; ACR. 2) ATIS NOT UPDATED IN A SPAN OF 15 MINS BLOCKOUT TO TKOF. 3) TIMELINESS OF RVR RPTS AND FREQ CONGESTION.