MDT FLT CREW EXPERIENCES POSSIBLE RWY INCURSION.

Narrative

THE PROB BEGAN WITH THE APU NOT RUNNING AND THE XBLEED PROCESS UNSUCCESSFUL. THE WHEELS UP TIME WAS RUNNING OUT AND ON-TIME PERFORMANCE PRESSURE FOR RELEASE TO ZZZ. THE TWR ASKING 2 OR 3 TIMES IF WE WERE READY; CLRED US TO TAXI ONTO RWY 20 AND HOLD SHORT OF RWY 29. THE TWR TOLD US TO STOP AND THAT WE DID NOT HOLD SHORT OF RWY 29. THE TWR ADVISED THAT WE HAD NOT HELD SHORT OF RWY 29. THE RWY MARKINGS ARE CONFUSING AND AMBIGUOUS AT THE INTXN OF RWY 20 AND RWY 29. WE LANDED ON RWY 29 EARLIER AND THE RWY LOOKS LIKE A DISPLACED THRESHOLD; SO WHEN I WAS TAXIING ONTO RWY 20 I COULD SEE WHAT LOOKED LIKE A HOLD SHORT LINE FOR RWY 29. THE RWY 29 MARKINGS LOOKED TO BE 50+ YARDS AWAY FROM RWY 20. 45 MINS LATE TAXIING OUT FOR TKOF DUE TO SWAPPING ACFT FOR MAINT. STARTED BOTH ENGS AND SHUT DOWN THE APU (EVERY MIN COUNTS); AND FINISHED THE BEFORE TKOF CHKLIST. THEN SWITCHING TO THE TWR; WHERE WE WERE TOLD OF A DELAY OF ABOUT 15 MINS; WE SHUT DOWN THE L ENG TO SAVE ON FUEL. TWR TOLD US TO START ENG AT 50 MINS PAST THE HR WITH WHEELS UP TIME OF 54 VOID TIME AFTER 56. WE REQUESTED A XBLEED START WHICH WAS UNSUCCESSFUL. POWERED THE APU AND USED IT TO START ENG #1. SIMULTANEOUSLY; TWR IS ASKING IF WE WERE READY TO GO; AT WHICH TIME I INFORMED THEM OF ADDITIONAL TIME NEEDED TO WARM UP THE ENG. THE FO WAS DOING THE AFTER START CHKLIST WHEN THE TWR INFORMED ANOTHER NEARBY ACFT THAT WAS READY FOR TKOF ON RWY 29 TO HOLD SHORT; AS THEY WERE GOING TO GET US OFF FIRST. THE TWR THEN GAVE OUR INSTRUCTION TO TAXI ONTO RWY 20 AND HOLD SHORT OF RWY 29 (ADVISING US AGAIN OF OUR WHEELS UP TIME). THE FO READ BACK THE EXACT INSTRUCTIONS. WITH ALL OF THE 'RUSH' ACTIVITY; I INTERPED THE INSTRUCTIONS TO BE TAXI INTO POS AND HOLD; AND I STARTED TAXIING ON RWY 20 SLOWLY APCHING THE END OF RWY 29 (ALLOWING ENGS TO CONTINUE TO WARM UP) WHEN THE TWR SAID TO STOP. I HELD MY POS HEADING STRAIGHT DOWN RWY 20; HAVING NOT YET MADE THE 90 DEG TURN ONTO RWY 29. AFTER THE TWR TOLD US TO STOP; I ASKED IF HE NEEDED US TO CONTINUE DOWN RWY 20 WHICH HE REPLIED NO TFC FOR RWY 29; NO PROB TO STAY AT OUR PRESENT POS. THEN HE ASKED IF WE WERE READY (THE FO TOLD ME THE TIMING ON THE ENG WAS FINE) AND I SAID WE WERE READY. THE TWR THEN CLRED US FOR TKOF.