How much time and at what frequency is best for maintaining technical skills and working out improvement ideas?

Currently, I block out 1.5 hours per week for "Improvements". In reality, I often cancel this appointment with myself and fill it with my key deliverables.

I know I should be spending some work time on improvements. I am struggling with the frequency and duration.

I basically break it down into two categories: Improvements and Skills maintenance.

In terms of improvements examples can be simple: update that template, make this spreadsheet easier, add a macro, etc. They can also be a bit more complex. For example, I read article x which made a great argument to implement y. I would use this time to work through the concept and see if it is something that I can practically apply. Lastly, there may be improvement ideas that are helpful but not directly in my deliverables. The company sponsors a great improvement ideas program. They reward ideas with prizes etc. For example, I am currently working on a new traffic/walking pattern in our parking lot between buildings to increase safety even though I am not in the safety department (Safety department is now involved and has authorized the concept development).

In terms of skills maintenance, I am going after stuff I don't want to forget. For example, I have attended six sigma training. In a previous role, I used about 50% of the concepts. In the currently role, I haven't used much of the concepts lately. In a perfect world I'd like to fill out my knowledge to get to 100% of the concepts and practice on a regular basis since I will, likely, again use these skills. Another example of skills maintenance is a training I attended on Problem Solving. Awesome training. They gave us about 400 pages of examples and concepts. I'd like to really be able to apply and understand all the documentation. In order to do that I'd like to be able to practice, read and re-read the materials on some regular basis so I can stay sharp,

I know these are long-winded examples, very specific to me. I wanted to give some detail as to what I am struggling a bit with. Certainly the deliverables in my goal document are the priority. At the same time, I don't want all the other flowers in my garden to die. I am wondering what others have done to try to alleviate this issue.