If the shop is 3 weeks back logged it suggests they are doing a good enough job so that they are somewhat overwhelmed. 3 weeks is about the max shops I've been in have been behind, generally this becomes self correcting. As shown by the OP not leaving their bike for service and as the seasonal demand wears on. However, I'll also add that as a shop wrench I really try to do the one item quick jobs in a few hours at least. This includes flat tires or a single and externally accessed adjustment. Like tightening crank arms, aligning bars with the ft wheel or a headset adjustment. If the shop is embarrassed with how quick a headset adjustment takes VS their service rate amount they should just take the bike in for a couple of hours or at worst overnight. Whatever it takes to get the rider to leave the shop for long enough to do the work without the rider having a reason to question the cost VS time aspect. (Remember, service cost isn't about the time only but also about skills, tools and liability). Andy