Tamsulosin doesn't last 24 hours, so you normally take it with the first meal of the day to cover day-time, or the last meal of the day to cover night-time. You must always take it with a meal, as that's part of how its slow release mechanism works. On an empty stomach, it can generate an overdose (which risks you fainting), and it runs out sooner in the day. Also be careful if taking any PDE5 inhibitors (Sildenafil, Tadalafil, Vardenafil, Avanafil), as Tamsulosin and PDE5 inhibitors are both uncontrolled short term blood pressure reducing tablets (it's a side effect), and if you take them at the same time, you also increase the chance of fainting.
As always, you might want to discuss with your GP, but at least you now have some background to understand how Tamsulosin works.