It all depends on what people want. If they want a bar, Mamaracha is not the place. It's more of a daytime cafe, nighttime restaurant. A bit of a poser place and very expensive (probably close to 30 pesos for a sandwich now), although the food is tasty. It's always crowded and there is usually a wait for a table, especially outside.
Sugar across the street at that time is not crowded and has a 7 peso happy hour on pints, wine or mixed drinks (disclosure: I used to own Sugar but now have no financial or any other interest in it). Much better chance of getting a table there that will accomodate people straggling in at various times. They also have pizzas, empanadas and picadas.
On Malabia on the other side of the park is a pizza place that's supposed to be good although I have not tried it.
Limbo Lounge (across the street and down Costa Rica a little bit from Mamaracha) might be a bit more flexible on the seating as well, but I don't know about the food situation there and it is quite small.
There's also the "brew pub" Antares on Armenia, but Friday night at that time it will be very crowded with the after work bunch.