After looking at my posted code I immediately saw the problem — it's solved! Here is the correct code to do it in case someone else has the same approach:
<$set name=weekday value=<<now DDD>>> <<list-links filter:"[contains:routine<weekday>]">> </$set> -- You received this message because you are subscribed to the Google Groups "TiddlyWiki" group. To unsubscribe from this group and stop receiving emails from it, send an email to tiddlywiki+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/tiddlywiki/150164eb-172d-41e0-838a-84dea6ec3bd3n%40googlegroups.com.