you are talking about.
Spell Tinkerer
The arcanist can alter an existing spell effect by expending 1 point from her arcane reservoir. To use this ability, she must be adjacent to the spell effect (or the effect’s target) and be aware of the effect. She can choose to increase or decrease the remaining duration of the spell by 50%. This ability can be used on unwilling targets, but the arcanist must succeed at a melee touch attack, and the target may attempt a Will saving throw to negate the effect. This ability cannot be used on a given spell effect more than once. This ability has no effect on spells that are instantaneous or have a duration of permanent.
Armored Mask
By expending 1 point from her arcane reservoir as a standard action, the arcanist grants herself an effective illusion of armor.
She gains the benefits of mage armor with a caster level that’s equal to her arcanist level and appears to be wearing light or medium armor of whatever design she chooses when activating this ability. At any time while this effect is active, she can expend 1 additional point from her arcane reservoir as an immediate action to also gain the benefits of shield of faith with a caster level equal to her arcanist level.
I have no idea on how to focus on them. One of them is basically mage armor. + immediate action shield of faith. this part is actually good.
Spell tinker is a worse extend spell pretty much and lowering an enemies buff duration is not that good.
If you want to focus on abjuration. Pick counterspell.