Is it better to have a longer time barber heart for more damage build up or shorter time for quick effect?

She said long

Seeing as they are pretty much disposable now, just trial and error to what suits you.

For speed run = short; Boss = long.

if you are weak, the longer timer can help you do more damage. if you are too strong, the longer timer can slow down your kills.
could keep 1 of each and use one for dungeons/farming and the other for bosses with alot of life

MYTH: You have to wait (2.0-4.0) seconds for mobs to explode, so lower duration barber heart is better for speedfarming, and higher duration is better for bossing.

FACT: Mobs explode regardless of time if they take enough damage that would have killed them. If you normally one shot mobs, they will die instantly. You don't have to wait (2.0-4.0) for them to die. Higher duration barber heart is ALWAYS* better to take as it'll have a higher ramp on bosses.

Unless you are playing a build without easy/consistent access to vulnerability and rely on an item or glyph to enable vulnerability on mobs. For example, some classes' Exploit glyph triggers vulnerability for 3 seconds on a mob on hit. You want your barber heart to expire just before your vulnerability on that target expires so that the barber damage will benefit from +vulnerable damage

Thank you great advice on that vulnerability aspect

2.9 seconds is the one to use, unless you can consistently apply vulnerable to mobs/bosses.

Lilith --> 4 sec
Rest --> 2 sec

2,9s is ideal since u can use the 3s vulnerable from exploit glyph

shoutout to roneye*