Weekday daytime is your best bet — these are working mechanics, not a call center, so if nobody picks up, leave a voicemail with your name, town, and what the machine's doing. Callbacks usually happen within a business day, faster in the off-season.
Off-season drop-offs are the single best move you can make. Snowblowers in September, mowers in March, boat motors before the opener — that's when turnarounds are days instead of weeks. Waiting until the first blizzard to discover the auger won't turn is a valley tradition, but it doesn't have to be yours.