The charge time might feel slow because you are currently using a bomb heated at 1 and not 10.
It seems odd as a bomber, but try and reach 3 pieces of medium CTR gear if you haven't.
I hope this helps change what you think about the charge time, I felt the charge time was where it should be :)
In order to hit turrets, you can actually clip them twice with a single bomb on the outer shards. Position the initial blast not ontop of the gun puppy, but rather a few blocks away from it. Then, the shards will take care of hitting it for you :3
Overall, not very many of the slower monsters like retrodes or lumbers etc. were a problem with me in how they moved into the no-damage zone of the bomb. The monsters that are fast, such as wolvers and gremlins, will be knocked back AND knocked down with the initial blast, then knocked down again with the outer blasts. Because of this, you will likely want to position the initial blast to hit wolvers and other fast enemies, but not always position the initial blast to hit slower enemies if they are resistant to knockback or do not get knocked down.
Basically, it is something new and something to get used to. Which will take a long time.
It helps to cloud your monsters by circling them and placing these bombs like triangles. You can basically do this mindlessly and a huge group of monsters will turn into shiny piles of loot.
I used this bomb and found it useful, and I highly suggest that you try using it again with a few tips I gave you.