Congrats on Nursing school! Been there done that - and lemme tell ya there really is life after nursing school - and then there is always grad school too - yup - I was dumb enough to go BACK!
What kind of schedule are you going to be working? If you will be working 3 12's a week, training for that 100 miler should be no problem. The first week - see how you do without killing yourself - ride a leisurely pace 3 to 4 times a week. Then just set a goal for yourself to increase your miles by 10 each week - 10 weeks will have you at 100 miles or more!
I have had about 9 weeks to train for the MS 150 - and that is what I have done - my goal by next week was to be riding 100 miles a week - This is my 100 mile week and Im doing 50 tomorrow!
And I started from NOWHERE and WAY out shape on a bike I didnt even have yet!
I wanna ride the 100 at the hotter n hell too!!!!!