I maintain a few small open source projects around publishing math on the web. I have a Freenode IRC channel and Matrix room bridged together where anyone is welcome to join anytime they need help. When I am relatively free, I also post a live web meeting URL to the channel where anyone can drop in or drop out anytime. So the Matrix/IRC channel along with occasional web meetings have been my version of office hours so far.
A wonderful side effect of maintaining a channel like this has been that there is a tiny group of regulars now in the channel and we often discuss stuff other than open source projects too. Due to the nature of the projects, they attract like-minded people into the channel, so a lot of time is spent in discussing mathematics and computer science literature, and Lisp, Emacs, etc. What started as a support channel has gradually evolved into a tiny book club for mathematics and computer science!
My comment was incomplete earlier and I edited it to update it later but you had already posted your comment before my edit, so posting this comment to clarify that I do occasionally indeed provide my full attention. I sometimes post a web meeting link to the Matrix/IRC channel. Anyone is welcome to drop in to the web meeting or drop out at any time. However, I have not tried the approach of offering one-on-one meeting slots via calendar booking and relying on audio/video during the meetings and that is something I am eager to try out now.
A wonderful side effect of maintaining a channel like this has been that there is a tiny group of regulars now in the channel and we often discuss stuff other than open source projects too. Due to the nature of the projects, they attract like-minded people into the channel, so a lot of time is spent in discussing mathematics and computer science literature, and Lisp, Emacs, etc. What started as a support channel has gradually evolved into a tiny book club for mathematics and computer science!