Is it true that, even though they process returns seven days a week, they only update the status on Wednesdays? Is that the only day the status will change on WMR?

No WMR is updated every 24 hours.

What time does it usually update?

IRS - Questions about Refunds
<a rel="nofollow" target="_blank" href="https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions">https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions</a>

Refund timing
<a rel="nofollow" target="_blank" href="https://www.irs.gov/individuals/refund-timing">https://www.irs.gov/individuals/refund-timing</a>