preparing vs getting ready

Yes

 You can, but I see it meaning something else.  "Getting ready" has a wider scope to its meaning.  You could do other things when getting ready that aren't directly related.  For example, use marriage instead of skydiving.  Preparing for a wedding might include sending out invitations and hiring a band, but getting ready might be something outside of the marriage itself.  You might have been invited to the wedding, and it's 2 hours before the wedding.  So, you are "getting ready" for the wedding by dressing up, but you aren't doing anything to prepare for the wedding at that point.  Maybe you prepared some dishes to bring to the wedding.  Preparation is more directly related to a certain task.

 With skydiving, maybe it's just minutes before the skydiver is about to take the big leap.  They are getting ready by checking their jumpsuit and equipment, but none of this is preparation.  Maybe they checked the weather in preparation for the dive to make sure the conditions were safe.  

 preparing is more formal and perhaps says that the process is more meticulous/detailed/systematic

 

Avangi

I took J's distinction to mean that "preparations" often begin well in advance of the event, while "getting ready" is usually done at the last minute.

(Perhaps he needs to obtain clearance to invade Canadian air space at an altitude of 25 miles.  If the Canadian Air Force shot down a French balloon, it could create an international incident.)

 

Time definitely offsets the meaning between preparing and getting ready.  Another example using time is track racing.  You might prepare for a race by running laps everyday, but when you run the actual race with everyone else you aren't preparing.  You are getting ready, getting set, and going!!!

However, time is not at the core of the difference.  As I see it, it's a matter of being direct or indirect.  To determine which action is direct or indirect, ask yourself "Would this event not take place if task T did not occur?" T = task needed in order for an event/desired outcome to occur

1. Skydiving - If the person skydiving doesn't check their jumpsuit or equipment, can the event still take place?  Answer: YES, therefore it's under the category "getting ready"

2. Skydiving - If the person skydiving doesn't buy a parachute, can the event still take place (assuming they still want to be alive the next day)? Answer: NO, therefore it's under the category "preparation"

3. Marriage - If you don't get the invitation cards out, don't buy the ring, and don't hire a band, can you expect there to be a wedding (defintion of wedding here would include needing at least those three parts, and you might want to get a bride or groom while you are at it )?  Answer: NO, therefore it's also under the category "preparation".

4. Marriage - If you don't buy a suit for your friend's wedding, it's 2 hours before the wedding, and there is no rental place which will give you a suit or tuxedo on such short notice, can the wedding still take place?  Answer: YES, therefore it is under the category "getting ready".

Here is an example of one where time is irrelevant I think.  Making a sandwich.  Do you prepare ingredients for making a sandwich or do you get ingredients ready?  In my opinion, the ingredients are essential for a sandwich to be made, therefore it is under the category "preparation".