[Si Coe]

Sadly ironic that you ordered stuff from JE Spares, who don't open on Saturdays either!

However its important to remember that most LHS's are small affairs with a limited number of staff. That means if they don't close for a day, they get no break - you work Monday to Friday but that means you get two days off so why shouldn't your LHS owner?
Some shops do it a little differently - Roundabout is open on Saturday but not on Monday, NW Model Supplies is open Sat but no Wed etc but ultimately they are open 5 days a week and there are days you can't shop there.
BMM are actually open 7 days a week, but the upshot is that staff service can be a little variable as they aren't all full time staff with lots of experience.

I like you find it impossible to get to a model shop mid-week, but I understand that that just means I need to use the internet. And for further irony my first port of call is normally DMS!