I spend as little time as poss and have done for years. Regularly do items on the same day. Did a SM Q&A off the cuff once when I forgot I had it and it was announced during the announcements. I had 10 mins to check it through in my KM.
I have done a number of public talks with just a few hours prep.
Do I feel guilty? No. Even before I saw TTATT I thought that most people could, if pushed on the doors, speak extemporaneously about most subjects. Most main points were as obvious as anything. Even public talks offer little depth, especially when on non prophecy based subjects. Anything about Jesus highlights love. Never fretted about it. Hopefully I will have less and less talks soon...
Ive always been commended for my talks het never poured over them for days and days. Most people could not tell you what was in the meeting 10 mins after it is over let alone worry about the detail of what you say.