Slight correction for 6:45 - While you can gain an extra walk in any day, you have to use the extra walk on the day you acquired that day bonus. So if you gain an extra walk on Friday, then that day bonus can only be placed on Friday (page 8. in the rule book).
Also, while it shows you placing the card at the bottom, you can actually place it at any point in the line of cards for that day. You'd only want to put it at the bottom if you don't want to do the last card's highlight and it can be a bit of a gamble as, like any walk card, you don't get to see it or the potential highlight the walk could provide as the last card in the line.
