Am I allowed to cut my hair tomorrow, Friday the 26th?
It is permitted to take a haircut tomorrow (the Friday before Lag Ba’Omer that falls on Sunday).
The Darchei Moshe (493:1) mentions two opinions concerning this question, the Maharil being stringent and Mahari Weil being lenient.
The Rema (2) rules that it is permitted, and does not mention the stringent opinion. The Be’er Heitev (6) notes the stringent opinion, but writes that where the custom is to be lenient, this is the halachah.
Sorry if this reply didn’t reach you on time (I now note there was a technical problem), and best wishes.