Drop in /Library/LaunchDaemons and disable TimeMachine's automated backups. Will run backups at 8:00 and 18:30, adjust by modifying the StartCalendarInterval array.

coop.plausible.backupd-daily.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>coop.plausible.backupd-daily</string>
    <key>ProgramArguments</key>
    <array>
        <string>/System/Library/CoreServices/backupd.bundle/Contents/Resources/backupd-helper</string>
    </array>
    <key>StartCalendarInterval</key>
    <array>
        <dict>
            <key>Hour</key>
            <integer>8</integer>
            <key>Minute</key>
            <integer>0</integer>
        </dict>
        <dict>
            <key>Hour</key>
            <integer>18</integer>
            <key>Minute</key>
            <integer>30</integer>
        </dict>
    </array>
</dict>
</plist>