Why are you asking this question?

You've presumably done the maths already. Only you know how many of you there are - but this tour costs £57 for an adult, compared with £41 for doing it the sensible way.

You're able to write out your question. So why don't you "know if the timing of the train and bus to get there in time for our tour and then the timing of the return would be problematic."? The Potter website explains where you need to get the train to and from, and how the bus from Watford Junction and back works. www.natinalrail.co.uk tells you there are fast trains every 10-15 minutes. But in case you've missed the fundamental point: neither the train nor the connecting bus at Watford needs advance booking.

The tour company website, admittedly, doesn't spell out how much slower the road connection from Victoria and the faffing about with checking in in advance (for a bus to Watford? The BA flight to New York from London City requires less time wasted on checkin) is than the proper rail route (though about 0.3 seconds looking at the company's schedule makes that blindingly obvious)

So you're asking for advice on whether it makes sense to spend 40% more on an inflexible, slow, busride than on getting to Watford the way everyone else does.

I repeat my question. Why on earth do you need advice?