“chasidim harishonim”
I checked the Artscroll Berachos on this and a wonderful insight is brought down.
The Gemara asks how their needs were done and their knowledge of Torah kept. The focus is on the term “kept” rather than acquired.
This implies that they had already fully acquired Torah previously and only then were able to become the “chasidim harishonim”. This is based upon the dictum that one who is deficient in Torah knowledge can not be a true chasid.
Based upon this, their spending 9 hours in Davening only occurred after they mastered Torah. Hence, the concern was only how they kept on to their Torah knowledge, and not how they acquired their Torah knowledge.