While attempting to schedule a weekly Pipelines to run on Sunday for example, Pipelines will schedule your build for Saturday for some reason. This happens for every day of the week too; Say for example if you schedule a build for Tuesday, it will display as if it was scheduled to Monday.
See the screenshots attached for further details:
The pictures above show that my Pipelines is scheduled for Saturday, where I actually selected it to run on Sunday. The time is correct, but the day is incorrect.