AN EMB145 PILOT FELT RUSHED BY LOCAL CTLR TO EXIT THE RWY. NOT BEING NIGHT VISION ADJUSTED AND RUSHED; HE PICKED A NON TXWY TO EXIT THE RWY AND HIT MUD.

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WE MADE A NORMAL APCH AND LNDG. IMMEDIATELY AFTER TOUCHDOWN THE TWR CTLR WAS YELLING AT US TO GET OFF THE RWY IMMEDIATELY. WE HAD PLANNED TO EXIT AT TXWY XB AND THIS STILL LOOKED LIKE THE BEST CHOICE. LOOKING AT THE ARPT DIAGRAM IT APPEARED THAT TXWYS X AND XB CONNECTED AT THE RWY (WE HAVE SINCE LOOKED AT A BLOWN UP PICTURE WITH OUR COMPANY AND SEE THAT THIS IS ACTUALLY NOT THE CASE). IT WAS DUSK AND WAS DIFFICULT TO SEE ANY DIFFERENCE BTWN THE PAVEMENT AND GRASS AS IT WAS GETTING DARK. WE PASSED TXWY X AND STARTED OUR TURNOFF (AGAIN THINKING X AND XB WERE CONNECTED). OUR TURN WAS PREMATURE AND WE WENT OFF INTO THE GRASS PARALLEL TO XB. BY THE TIME WE REALIZED OUR MISTAKE; WE WERE UNABLE TO STOP OR TURN. ONCE IN THE GRASS; WE NOTIFIED ATC AND TRIED TO TAXI OUT BUT WERE STUCK. WE HAD A TUG COME OUT AND THEY PUSHED US OUT AND PULLED US TO THE GATE. WE MADE SURE THAT NO ONE WAS INJURED AND THERE WAS NO KNOWN DAMAGE DONE TO THE ACFT ASIDE FROM MUD ON THE GEAR. CONTRIBUTING FACTORS IN THIS INCIDENT WAS THAT IT WAS GETTING DARK AND HARD TO SEE DIFFERENT FEATURES OF THE SURFACE ON THE GND. MY EYES HAD NOT ADJUSTED EITHER (NIGHT VISION). I ALSO BELIEVE THE FRANTIC AND ERRATIC CALL BY THE CTLR LED US TO BELIEVE WE NEEDED TO EXIT THE RWY ESPECIALLY QUICKLY. IN THE FUTURE; I WILL TRY TO ENSURE MY PROPER POS ON THE RWY/TXWY. I ALSO WON'T LET AN IMPATIENT CTLR ENCOURAGE ME TO EXIT OFF THE RWY ANY EARLIER THAN I'M FULLY READY TO.