Damage Overtime is always a fun way to play Action RPGs, let’s take a look at how this mechanic works for Neocore’s Warhammer 40k Inquisitor Martyr.
There are Three versions of Damage Overtime, Poison and bleeding from physical attacks, and burning from heat attacks.

The patch from the Season of the Warp Surge drastically changed how damage is calculate from Damage overtime.

The DoT debuff deals 80% of your character’s Base Damage per second for 3 seconds, stacking up to 5 times for a total 400% of your base damage per second. This damage can’t crit, but if the skill itself crits, the damage over time will do more damage based on your critical hit strength. Every crit rolls 1-100 and adds your critical hit strength to that roll to determine the extra damage dealt, if you roll above 86, applied DoTs will deal 100% more damage, and anything above 136 makes them 200% stronger.

Most skills with the DoT effect will apply 1 stack per hit, skills with a higher cooldown will apply multiple stacks per hit. There are a lot of Item Enchantments that let you apply damage over time with any skill.

Any damage bonuses you get on your gear or passives has no effect on DoT, unless it specifically says so. The ancient Relics of Boiling, Trauma, and Toxins will give large bonuses to Burns, bleeds, and poisons.

The perk “Enhanced Attrition” let’s you go full into a DoT build by sacrificing 50% of all your non-DoT damage to get a 150% damage and 3 second bonus to all of your DoT Effects.

A really strong Psalm code Doctrine to scale damage overtime is this 5-piece that makes each vulnerability stack have 300% increased effect on DoTs. There’s also Doctrines that spread your DoTs to nearby enemies for more AoE.

I hope this was able to answer all of your questions about Damage over time, and inspired you to work on your own DoT build! Honestly, it’s in a pretty bad spot right now, it requires a lot of very specific enchantments on gear to make work, but it is still a ton of fun to play, just good luck doing anything above 10 difficulty with it.