HS25 IS SLOW IN RESPONDING TO DSCNT CLRNC FROM FL370 IN ZDV AIRSPACE.

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WE WERE CRUISING AT FL370 WHEN CAPT DECIDED TO LEAVE THE COCKPIT TO USE THE RESTROOM. AT APPROX THIS TIME; I HEARD ZDV DISCUSSING SOMETHING ABOUT ALT WITH AN ACR. THE ACR Y CREW TALKED ABOUT A LOSS OF HEADWINDS BUT THE CONVERSATION WAS VERY 'MATTER OF FACT.' I DONNED MY MASK; AND CAPT GOT UP TO LEAVE THE COCKPIT. AS HE STOOD TO LEAVE THE COCKPIT; CTR CALLED ME AND ASKED FOR A 20 DEG TURN; AND FOR ME TO DSND FROM FL370 TO FL360. AGAIN; THERE WAS NO URGENCY INDICATED BY THE TONE OF THE REQUEST; NOR THE TERMINOLOGY. AS THE CAPT WAS GETTING OUT OF HIS SEAT; I DID ANSWER THE CTR CALL. IT TOOK NO LONGER FOR CAPT TO GET OUT OF HIS SEAT THAN USUAL; AND I INITIATED A TURN ON THE AUTOPLT; AS HE FINISHED MANEUVERING PAST ME. I THEN RESET THE ALT ALERTER. THE FLT WAS PLANNED AND FLOWN AT HIGH SPD CRUISE; AND THEREFORE WE WERE WITHIN A FEW KTS OF VMO. I REDUCED PWR ON THE ENG TO SLOW DOWN BEFORE INITIATING A DSCNT. BECAUSE THERE HAD BEEN NO MENTION OF URGENCY; AND BECAUSE MY CAPT HAD BECOME A STANDING PAX; I MADE NO ATTEMPT TO DO THIS QUICKLY. I INITIATED THE DSCNT ON THE AUTOPLT; USING FLC; (WHICH WOULD HOLD THE CURRENT SPD); AND REDUCED PWR SLIGHTLY MORE. ZDV SAID THE INITIATION OF OUR DSCNT TOOK APPROX 1 MIN. IF MY UNDERSTANDING IS CORRECT; THE CTR INSTRUMENTATION DOES NOT SHOW THAT WE HAD LEFT ALT; UNTIL WE HAD CHANGED 300 FT. SINCE I HAD REDUCED PWR AND SPD SLOWLY TO ALLOW FOR A SMOOTH CHANGE; AND HAD INTENDED FOR NO MORE THAN A 1000 FPM CHANGE; I DO NOT DOUBT THEIR NUMBERS AT ALL. AS I APCHED APPROX 36550 FT THE CTLR GAVE ME A CLB BACK TO FL370; AND I BELIEVE IT WAS RIGHT THEN THAT HE GAVE ME DIRECT TO VHP. A SHORT TIME LATER; THE CTLR CALLED THE ACR Y ACFT; AND TOLD THEM TO CONTACT ZDV WHEN THEY LANDED. A SHORT TIME AFTER THAT; HE CONTACTED US AND TOLD US TO CALL ZDV ALSO. HE APOLOGIZED AS HE DID SO; AND SAID SOMETHING ALONG THE LINES OF; 'I CAN'T SAY YOU HAVE DONE ANYTHING WRONG; BUT I DON'T SEE ANYTHING.' WE CALLED ZDV; UPON LNDG. ALTHOUGH THE ZDV SUPVR SAID THIS WOULD GO NO FURTHER; SHE INDICATED WE MIGHT HAVE HELPED OUT THE OTHER ACFT; HAD WE INITIATED THE DSCNT QUICKER. IF THAT IS SO; I CAN ONLY SAY THAT I WOULD ONLY HAVE CHANGED THE ACTIONS I TOOK; IF I HAD KNOWN THE SIT WAS DIFFERENT THAN WHAT I WAS LED TO BELIEVE BY THE VERY MATTER OF FACT CONVERSATION BTWN THE ACR Y AND THE CTR; AND BY THE TERMINOLOGY GIVEN BY THE CTR. AT SOME POINT; THE CTR INDICATED THAT WE CAME WITHIN 2.9 MI. WE DID NOT RECEIVE ANY TCASII ALERT OF ANY TYPE; AND I SAW NOTHING ON OUR DISPLAYS; HOWEVER; I DO NOT KNOW OR REMEMBER FOR SURE WHAT RANGE THEY WERE SET TO.