Who told you have shin splints? If it was someone who just said it sounds like shin splints, ignore it until you have a proper diagnosis, until then chill as you still have 3 months. Carry on with what you can do, swimming, aqua jogging, core work etc.
My pain was in the front shin muscles, it was manageable if I walked slowly but if I tried to up the pace let alone try a run I'd be in agony, it got so bad I couldn't walk a 100 metres. This pain would subside after a couple of minutes rest. After the Op my calf's both complained due to the increase in flexibility but that's quietened down to a point that I'm jogging on a trampet and looking forward to starting light jogging soon.
I had to go private using the Spire Hospital Cardiff, I had both the shins done back in November, I was back on the bike in a couple of weeks (lightly) skiing in January and I'm walking pain free again
I was down for the 186 miles, but decided at the splitting point that I just did not feel like it, so ended up doing the 140 mile option, the last long climb up the Black mountain was a killer into that headwind, and then the heavens opened up just as I was getting back to Margam park, perfect timing