You might notices changes sooner than that, June. I hope so.
It'd probably be a good idea to start the folic acid at least a day or two before the injection. You might want to check whether you're supposed to take it on the day of injection itself: doctors can have competing ideas on that issue.
It'd be a good idea to drink lots of water the day before each injection, and you also might like to make sure you have mint / ginger tea etc in the house, just in case you get queasy. Oh, and I reckon you should get yourself a video too, as a reward for taking this huge new step
.