You can sort of work on HW and SB in tandem. The big hold-up for HW are poetics for stuff like Umbrite and Aether Oil. Yet, you get a plethora of poetics from running NM/FATEs in Eureka. So while you earn Eureka crystals towards relics, you pick up poetics to spend on HW. HW relics can be completed in a few hours if you factor in the incidental poetics you get from Eureka.