Tapas - Reservations?

Tapas are meant to be eaten at a bar with a drink thus by their very nature are not something that requires a reservation however there are plenty of restaurants that serve tapas to be eaten as a meal (think 'small plates' concept) and therefore some restaurants may warrant a reservation. As you intend to have a drink and 1-2 tapas then you'll be looking at the bar scenario and thus no reservations required.

When's the best time to have tapas? That's entirely subjective. I don't like crowds and noise so I wouldn't visit during busy periods but other people enjoy the atmosphere of a bustling tapas bar. For me, if a place is open and quiest then that's a good time for a drink and some tapas, others will think otherwise.

None of the good tapas/Pinxtos/Racione bars I went to have even thought of taking reservations. By nature, it can get crowded and you need to elbow your way in a bit, or go in the off hours. Some places do limit the number of people in the bar, so a queu might form outside. Some bars that also have table service might take reservations, but that would be more for a meal, not a drink and a snack.

For an authentic tapas bar, reservations are not required. People will typically eat tapas sometime after work and before dinner. So between 5:00 pm and 8:00 pm is typical.

Having tapas, or having pintxos (a different concept), is a social thing. You are not having a meal, you´re not nourishing, you are socializing with friends and/or family as part of the ritual of going out before lunch or dinner while having a glass or wine or a "caña" or "zurito" in the Basque Country (a small beer). Locals have tapas normally at the counter, pintxos always standing, you do not make a reservation as it´s not a restaurant but a bar and it´s totally informal.