ACR TAXIES WITHOUT CLRNC ASSUMING THAT TWR WAS NOT OPEN AT SAN LUIS OBISPO; CA.

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OUR FLT WAS A FLT FROM SBP TO LAX; SCHEDULED TO DEPART AT XA00 LCL TIME. DURING THE COCKPIT PREFLT DUTIES THE CREW NOTED THAT THE TWR FACILITY WAS CLOSED. CLASS 'G' OPS WERE IN PLACE. AFTER THE ENGS WERE STARTED AND WE WERE READY TO DEPART; I CHKED FOR A CLR TXWY TO MY CHOSEN RWY; RWY 11; AND BEGAN TO TAXI; THINKING THE TWR WAS CLOSED. IT QUICKLY BECAME APPARENT; HOWEVER; THAT THE TWR WAS OPEN. IT HAD OPENED AT XA00. WE PULLED ONTO THE TXWY AT XA04. WE QUICKLY CALLED GND CTL; EXPLAINED OUR CONFUSION ABOUT THE OPENING TIME; AND RECEIVED A CLRNC TO TAXI TO RWY 11. WE ALSO OFFERED OUR APOLOGIES FOR HAVING ENTERED A CTLED TXWY WITHOUT A CLRNC. PART OF THE PROB IS THAT OUR PRIMARY ARPT FACILITIES DIAGRAM IS PROVIDED AND THEY DO NOT PUBLISH THE TWR OPERATING HOURS OF ANY ARPT ON THE CORRESPONDING ARPT DIAGRAM. THE ONLY WAY TO FIND IT IS BY LOOKING AT AN ENRTE CHART DIALOGUE BOX FOR HOURS OF OP. THIS IS NOT A USER-FRIENDLY MEANS OF ACQUIRING SUCH CRITICAL INFO. HOWEVER; IN RETROSPECT; I SHOULD HAVE LISTENED MORE CLOSELY TO THE ATIS BROADCAST; WHICH GIVES TWR HRS OF OP WHILE THE TWR IS CLOSED.