Question:
If I had in mind to daven 2 shmoine esras by shachris and I forgot and remembered before mincha. Can I still daven it.
Answer:
From your question I am assuming that you are davening two shemona esrei’s because you missed maariv. The halcha is that it is only possible to “make up” a shemona esrei right after davening the shemona esrei of the next teffilah. Meaning that right after saying the shacharis one we say another one as a tashlumin for maariv. If we missed it by shacharis it can not be made up anymore.
Best wishes
Sources:
Shulchan Aruch O:CH 108-4.
