I happen to have just completed another Heavensward relic for glamor purposes. So your ability to complete it will depend on your own level and what you have access to, but... to answer one question. No. It can not be completed solo.

At level 80 I was able to do MOST of the completion for the weapon solo, however, the final step of the process requires you to do a victory lap of sorts completing all the primals, and Bismark is not possible to complete solo. Even at level 80, the sanua adds in that fight take basically zero damage if they're not kept seperated, so you'll need a friend to help for at least that step (or complete it in duty finder)

Beyond that, I can say I was able to complete the weapon in about a week. The steps definitely take a lot less time nowadays than they did back when they were current for sure.

Also, I would mention at this point if you want to complete it completely solo, when it comes to farming light, I would recommend doing this in Brayflox Hard Mode. You can do it faster with a team in Alexander Savage, but if you're going by yourself, then Brayflox is your best light for your time spent.