AS ROG said, if you’re having Tuesday off you will start a new six periods of 24 hours when you start work on Wednesday, so basically you’re starting a new working week on Wednesday.
If you don’t have Tuesday off the six 24 hour periods will begin when you started work on Monday, so if you did Monday on Domestic regulations then went onto EU regulations Tuesday you would need to start a new weekly rest period no later than 144 hours from when you started work on Monday.
If you don’t have Tuesday off Mondays work and driving under domestic regulations will count as other work for the EU regulations.