Below is my recommended amount of time per subject given the subject or material.
Mathematics
AP Calculus or College level: At least a session of 60 to 90 minutes. Calculus: At least a session of 60 minutes. Pre-Calculus: At least a session of 60 minutes. Algebra II: At least a session of 60 minutes. Geometry: At least a session of 45 minutes. Algebra: At least a session of 45 minutes. Pre-Algebra At least a session of 45 minutes.
Essay Writing
Grammar:
At least a session of 45 minutes.
Vocabulary: At least a session of 45 minutes.
Sentence Structure: At least a session of 45 minutes.
Science
AP Physics or College level: At least a session of 60 to 90 minutes. Physics: At least a session of 60 minutes. Chemistry: At least a session of 60 minutes. Biology: At least a session of 60 minutes.
SAT or ACT Prep
SAT Math At least a session of 60 to 90 minutes. SAT English At least a session of 60 to 90 minutes. ACT Math At least a session of 60 to 90 minutes. ACT English At least a session of 60 to 90 minutes. ACT Science At least a session of 60 minutes. Optional Essay At least a session of 60 minutes.
College Application Prep
College Selection: At least a session of 45 minutes. Application Advice: At least a session of 45 minutes. Supplemental Essays: At least a session of 60 to 90 minutes.