Hello. My wife and I just bought an older house and are having a plumbing problem that makes no sense to me. In 1 of the bathrooms the toilet and shower clog (when flushed, or running water). However it only seems to happen in the evenings. I turn off the water valve on the toilet and the water is down by the morning. Same with the shower, it drains by morning. But then I can use both as normal in the morning without any problems. Seems like a septic clog but only late in the day? Does that make any sense? Thank you in advance for your help.

Assuming that you are on a municipal sewer system and not a septic system.
You have a partially blocked sewer line and that blockage is a long way away form the shower and toilet.

During the day with your normal activities you are using only as much or only slightly more water than can pass through the blockage. That water gradually backs up in the pipes but not so much for you to know it. During the evening hours the use of the toilet and the shower along with other usage is more than can pass through the blockage and shows up in the shower and the backed up toilet.

The time of day is not the factor, it's the increased usage during the evening makes the partial blockage show up.

Snake the main drain line. Probably have to snake all the way to the street.

Assuming that you are on a municipal sewer system and not a septic system.
You have a partially blocked sewer line and that blockage is a long way away form the shower and toilet.

During the day with your normal activities you are using only as much or only slightly more water than can pass thru the blockage. That water gradually backs up in the pipes but not so much for you to know it. During the evening hours the use of the toilet and the shower is more than can pass thru the blockage and shows up in the shower and the backed up toilet.

The time of day is not the factor, the increased usage during the evening makes the partial blockage show up.

Snake the main drain line. Probably have to snake all the way to the street.

Sounds like a logical explanation. Thank you for your help. I'll give that a try.