internet is only good at night

I believe it depends upon where you are and how much traffic is channeled through the tower. To know more you should use a browser and go to the web UI (192.168.12.1) from a local client. Knowing the 4G and 5G NR bands and the performance of the signals is helpful. It helps set expectations and provides clues as to why it is slow or fast. Compare the reporting of the router web UI when it is good to when it is slow. Take screen clips and store them in a document to record what you learn.I made a one page document to share with others that might not understand the information. You might find it helpful. At least you will have possibly a better understanding of how the router is working and be able to ask the right questions of a T-Mobile support engineer. If you have data about the operation and post some of the facts about the router operation there are numerous people responding to the forum that can possibly help. Some people will commiserate with you and others will try to help. It does help to contact T-Mobile support and let them know there are problems in a given location. If others on the same tower are experiencing similar behavior and they get enough calls then they tend to look closer at a tower and the operation. It does take time so patience is necessary. Been there done that. Once they identified the problems they fixed it here and it has been better than it was.