Over at Legion, we're hiring for a couple of open positions right now, which means I'm spending most of my two days a week there parsing resumes and doing phone screens. Over the 11 years I've owned Legion, I've done hundreds of phone screens and interviews, and the most important rule that I've followed the entire time is that if you aren't on time for your interview, you don't get one. No matter how much I like someone, or how well they've done at previous steps in the interview process, if they aren't on time for an interview, we (politely) tell them to hit the road.
There are several reasons for this rule, some of which are specific to my company, and some which are good for everyone. First, at Legion, we move freight. Our ONLY job is to get things where they need to go, on time and in good condition. Our customers do not tolerate lateness for their freight, and we don't tolerate it from our employees. It is important for everyone to understand that, from the first interaction they have with us on. (We even have a special award for people who are late to our staff meetings—it's a horse's ass. We find that winning that trophy once usually cures someone of their tardiness, permanently.)
Second, for me, being on time is a demonstration of respect. Being late implies that your time is more valuable than that of the person you are meeting. If you've agreed to meet someone someplace at a certain time (whether in person or in the virtual world), you should be there on time, if for no other reason than to respect the other person's time. As busy as I am now, I do not have time to waste waiting around for someone who is trying to get me to hire them.
Third—and this applies to everyone in the world, whether you ship freight or not—I believe that interviews represent what I call "first date behavior". I've dated a fair bit in my life, so I'm pretty familiar with the rituals involved in first dates. Best hair, best makeup, that outfit that ALWAYS works, your good jokes, etc. Now that I've been with my husband three and a half years, he's lucky if I comb my hair before we go out. Same goes for new employees. They are going to present the absolute best version of themselves in the interview process, and if that version can't show up on time, they sure as hell aren't going to be on time to work every day. Especially if I accept that behavior right from the beginning.
Now, I'm sure you'll ask, "but what about traffic/directions/technical difficulties?" Plan for them. Give yourself extra time. Test the tech before you have to use it. And if you have an issue, if you've "arrived" five minutes early, you can get on the phone and call the person you are supposed to meet and let them know what's going on. I give a lot of grace to someone who calls me in advance of our meeting to say they are stuck in a huge traffic jam (I live in Cincinnati, there's always a huge traffic jam) or their Zoom isn't working, but they are going to fix it as fast as they can. What I don't have patience for is the person who emails me 45 minutes after we were supposed to meet to let me know their Zoom crashed or they got lost.
So, yeah, I'm a hardass about this stuff in the interview process. I have high standards. You should, too. You should set the ground rules from the beginning and stick to them without apology. It is your company, your process, and in the end, your responsibility to make sure these rules are followed. Wavering during the interview process just makes it that much harder to enforce your standards once someone joins the team.