Eurostar to Belgium

Yes, it is usually on time (within +/- 5 minutes), sometimes it is early. There is one train every 1-2 hours, so there is plenty to choose from.

Buy tickets here: https://www.eurostar.com/
Tickets for next April are already on sale. Book soon to get the cheap fares. For 28th April 2018 they are currently quoting (2nd class):

Depart 06:57 arrive 10:05, 64.00 €
Depart 08:58 arrive 12:08, 64.00 € 3 tickets left at this price
Depart 10:58 arrive 14:05, 50.50 €
Depart 12:58 arrive 16:08, 50.50 €
Depart 15:04 arrive 18:05, 77.00 €

It is very reliable. You will be fine.

Just another answer to support Chris's and Frank's responses to you.

Enjoy!

Really, not trying to be a contrarian but I, personally, would go in the day before. In almost all of my Rick Steves tours there has been someone who's transportation was slightly disarranged and missed the first night meet-up or a time or 2 the first day of the tour. There is also generally plenty to see in the cities where the tour start!

I have taken the Eurostar London to Brussels only once and as others indicate it did run on time. However I took the Eurostar from London to Paris a few years ago the day before my meet up with the Paris and Heart of France tour and it ran 101 minutes late due to a cable theft on the line (according to the announcements on the train). That trip seemed to be prone to train problems as my train from York to London was cancelled because it hit a horse on the tracks then the one we got on leaving York was severely delayed because of a broken rail. I was glad I had gotten stuff for lunch to eat on the train. We wound up with about 3 train's worth of passengers so many had to stand most of the way in to London and it was nearly impossible to pass thru to the food car.

I have also taken the Eurostar several other times either London-Paris or Paris-London with no problems.

I am very risk averse and want to be in place the night before a tour. To me, the fact that you posted this question means you are maybe a little worried about it working out and that alone would make me want to be in place the night before.

....and yes, I've got reservations in Canterbury the night before the Villages of Southern England starts next year and in Edinburgh the night before the Best of Scotland starts, lol!!

I'll also add that there is ~never~ enough time to see things in London. A lifetime would not be enough time.

I'm in favor of arriving a day ahead for a cruise, but the penalty for being late to a Belgium land tour is very small. I say that even though I once had a Eurostar delay of 8 hours, for a track fatality in France. I was lucky they held the last train towards Antwerp, or I would have spent the night in Brussels.

Will we be safe to take the 7am or 9am train on April 28?

What do you mean by safe? Are you referring to your personal safety or safe as in being able to catch the train in the time frame you have?

If it's a personal safety query then you really have nothing to worry about. At that time of day most of the passengers will be professionals travelling to work. Even then, whatever the time of day here are never any safety issues.

Thanks everyone for your answers. Although I am usually in favor of arriving a day early for a tour, I am taking a chance and we are staying until Saturday!