Whenever we create karma, it is under the law of dates that decides when karma will manifest. Not every action meets immediately its reaction, or not every cause immediately meets with effects. The law of dates inherent in karma decides the time. Sometimes karma is met five lives later or is met in three months or instantaneously. To know the dates of manifestation of karma is beyond our ability as it is entered into the computer which processes the group, national, global, and Cosmic karma - together with our individual karma related to the rest.
There is the opinion that our karma is final and nothing can change it. This is a superstition. We can change our karma. We can improve it, even totally erase it by actions that are sacrificial, heroic, all-inclusive. Even in a dire situation a bad karma can appear as a feathered friend if you lead a sacrificial and intelligent life.
We must consider our karma as a chemical compound. It is possible to change its chemistry using chemicals that change it, dissolve it, or render it totally beneficial.
Chemicals are not only physical elements. They are also heroic actions, sacrifice, devotion, dedication, lofty thoughts, unconditional love, spatial ideas, and supreme striving. Such chemicals have power to change the compounds of our karma.
Karma & Reincarnation, p.168