Here is what I would do:
1. Make the must for your second batch.
2. Rehydrate the rest of the yeast for only 20-30 mins and then add 1/4 cup of the must from this second batch.
3. After two hours add another 1/2 cup of the new must.
4. After another two hours add 1 cup.
5. After another two hours, pitch into your new batch.
6. Add nutrient to your original batch.
7. After 12 hours or so, combine the batches.
You can push this further, step-feeding in two hour increments before combing the batches, but for 2 gallons this seems like enough.
You may have done some damage to the yeast from your first batch. I have no expert knowledge on this part, but 2 hours is much longer than I have ever rehydrated yeast, without step-feeding, and is much longer than Lalvin recommends.