As someone with all of the relics from HW-current.
I would say it... depends.
It depends on the order you do them in, and how you best make use of your time, really whilst doing those relics.
For example, whilst doing the SB-ShB relics/Bozja you will naturally accrue plenty of poetics which will narrow out most of the grind from the HW relic series. Like, would you really want to do those, just to them find out that Eureka and Bozja hands you the tomestones on a silver platter.
Even when doing the SB relics - If you do every relic for each stage before moving onto the next stage then you do burn a lot of time and resources doing this. e.g., spending time tracking the big NMs cam help reduce how much time you spend in each zone, and whether you find it worthwhile spending a lot of time just waiting for respawns, when you could be doing another zone.
Equally can help actually planning across multiple relics, and doing multiple steps in tandem. This can save a ludicrous amount of time comparative to one step at a time. This is especially the case for the ShB relics, when you can work on several stages at once by doing the same activity, e.g., Delubrum Reginae. Even something as simple as doing both memories of the dying steps at the same time in Bozja can be a great hand in saving time.
I wouldn't even go as far to say do the ARR relics before doing the HW relics and so forth. It's a big time waste, since there are steps in the ShB relic that allows you to effectively skip the same step that trading the Zeta relics for the first step of the HW relic otherwise would, so there's overlap in this regard, depending on how you do the memories of the dying.
Progressing the ARR Zeta relics is also a great way to burn time between Eureka zones, and when there's downtime in Eureka, e.g., no NMs up.
Another example is the Alexandrite step for the Zeta relics. - If you're able to do the Endwalker relics, and especially by hunt trains, and just doing S-Ranks generally then you will find yourself getting a lot of Allied Seals which you can use for this, not to mention Tomestone of Poetics as well.
To keep it short, doing a lot of the relics in tandem will let you save a lot of time, if you're able to plan adequately for it. This does also imply that you are doing all relics from a given expansion and not just 1 relic from each expansion. But even in this case I would say doing some activities in tandem, and planning ahead can make a big difference, especially with poetic farming.
Edit: They can take dreadfully long if you aren't respecting your time, or how efficiently you can do them. But they can be very short and very easy if you are respecting your time. I did the SB relics before doing the HW relics, and doing it that way effectively just allowed me to skip a tonne of poetic grinding.