Question: I applied for a job and during the various stages of the job interview the hiring person told me that they will get back to me in a certain amount of time. However, after every round of the interview the hiring person overstepped that limit. One week turned into two, two weeks turned into five. **And this happened after every single interview round.**

Even though the job sounds interesting and is with a reputable company, I wonder how they will treat me on the actual job if if they overstep their maximum allotted time to respond to me after every single interview round.

The position I'm applying for is relatively new in the company, so I think they're taking their time with the job applicants, but still, overstepping the time limit to get back to me on three separate occasions is non-professional to say the least. They also didn't acknowledge the delay.

**Should I consider this kind of behavior a red flag?**

Answer: 
Yes and no.

Yes since in normal times it would be obvious that you should get a proper estimate. No since hiring in Corona times may be more complicated and subject ton constantly changing rules (e.g. is there anybody on furlough who could do the work, prove to your boss that you checked, prove to working council that you believe it....)
I would say that unless you apply for a job, the quality of their HR is not that important. Look for red flags with the people you are working with, they are more important. You can get an excellent job in a company with rubbish HR.