Starting descent just after level off when the flight attendant is aware that there is an hour to go would be extremely suspicious.
That is actually not all that unusual. Descends and climbs happen, quite often in fact, especially in europes pretty crowded airspace. They usually do know how much time they have for their service, the rest usually not. Had the case once where we climbed to 410 and then had to descend down to 200 right away just to get out of turbulences. Nobody ever asked what we were doing or why we were so low. They never noticed the descend, just that the turbulences weren't as severe anymore.