Guild Wars 2

Damaging conditions tick every 1s. If one is using -condi runes or food and a 1s condi is applied, does it not tick?

If it’s the only condition applied, that is correct, it will not tick. If there is another ticking condition already on you, like bleed or poison, it depends when between ticks the 1s condition was applied.

This page may be helpful: http://wiki.guildwars2.com/wiki/Conditions

As I understand it, a stacked condition may last for 10 seconds, and a -Condition food (say 10%) would affect that condition so that it lasted only 9 seconds then.

These are just arbitrary numbers, but you get the idea. Duration, or the reduction of duration is rounded to the nearest quarter second. I think, anyway, I’m not an expert on condition removal.