In the madness of youth and dieting, I used to take a LOT of Sennakot, more than 8 tabs daily. They ruin the motility of your bowel so you will have to persevere in trying lots of options.
Now in my 60's, I chew a M.....isons antacid tablet (have Calcium Carbonate in them) last thing at night with a glass of boiled water and then next morning, a hot cup of tea usually does the trick.... (before any medication)
Blood pressure tablets are to be taken before 10am to lower your blood pressure throughout the day.
One of the ways they work is by lowering the kidneys fluid retention threshold, so any daytime drinks will be flushed out, lowering your blood volume/blood pressure. So there's less water in your lower bowel. Your lower bowel needs water to bulk your stools or they will be bullets. The larger bulk, the more easily passed.
Drinking water before bedtime will help replenish your blood fluid levels as the tablets have a short half life so bowel osmosis will improve overnight.
Perhaps just google how the GI tract works and it might help as I probably haven't explained well.
But certainly when on BP medication, your most effective fluid intake will be evenings.
Good luck