Individual work on strategy, competition, positioning, partnerships, hiring - 4 hours
Working as part of the company executive team (meetings, 1-1s, alignment) - 4 hours
The above can range from 10 to 40 hours per week based on the size, maturity, complexity and growth stage of a B2B SaaS company. The quality of the people on the marketing team will improve over time and help reduce the investment needed as the engagement progresses.
The different stages require a different approach. The above is a good overview though.