It is impossible for us to figure out how long your mom will live. Do remember, that it is quite likely that you will be able to visit for a short while on day 5 (with nobody noticing there is something wrong with you) and rather likely that you can do long visits on day 7 (many implantees with a desk job are at work by day 7; though it is best to plan to be back at work at day 14). So you will not be "away" for very long.
also, I totally agree regarding the comment by larry10635 that nobody should know unless they must know. There WILL be family members who will hold it against you that you had "elective surgery to enhance your dick" during mothers illness. Those family members are wrong to judge, but judge they will, so you need to mitigate against that by keeping a secret.
In my opinion, you should get the surgery in two weeks; facing "the knife" takes real courage; you might not have that courage later in the year.....so, do not stop that rolling freight train.
"Strive hard to find the best implant surgeon -- surgical experience really matters"
(55 yo with Titan 22cm implant Feb 2017 by Dr Eid) Great experience -- I'm super pleased with my length and girth and implant performance.