Great job! Only stylistic points to mention. yay!

I keep thinking about this line:

puts "1: Monday, 2: Tuesday, 3: Wednesday, 4: Thursday, 5: Friday, 6: Saturday, 7: Sunday or Q: Quit"

It's not bad --- but it does repeat some information. Like the WEEK_DAY above as a constant. I might do something like:

COMMANDS = {"Q" => "Quit"} 
all_choices = WEEK_DAY.merge(COMMANDS)
puts all_choices.map{ |k,v| "#{k}: #{v}"}.join(" or ")

Then later, you could do something like

day = select_day

if all_choices[day].nil?
  puts "invalid choice #{day}, please try again"
  next
end

Unsure if that really makes it better not, but wanted to show an alternate flow.

I think you are right. I especially like all_choice[day].nil?. It can replace my ugly regex!

BTW, I also finished the assignment of Episode 2. Can you check my code?

Thanks, @jwo