Minimum time between two servings of whey protein isolate?

The study at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3197704/ concludes (emphasize mine):

We suggest that instead of a single, large protein-rich meal, ingestion of multiple moderate-sized servings of [...] protein-rich foods over the course of a day may represent an effective means of optimizing the potential for muscle growth [...].

Question: How much time should I leave between two "servings" of whey isolate?

Context

Calculation tells me that 5 or more servings are best for me (muscle gain, 75kg, 186cm). Problem: I only eat 3 meals per day, and for various reasons I can't eat nor drink anything but company-provided water during business hours (10am-12pm, 2pm-9pm). In other words, my only free time is like 1.5 hours in the morning, 1.5 hours at lunch, 3 hours in the evening. I am afraid that 1.5 hours between two servings would be too short and would equal a single large serving, ie mostly wasted.

• Given your limited eating schedule you may want to try other (slower absorbing) types of protein like casein or egg.
– Dan
Commented Jul 9, 2019 at 19:27
• @Dan Thanks for the tip! Would you mind posting an answer explaining how to calculate my optimal casein/egg serving size and number of servings?
– nic
Commented Jul 10, 2019 at 1:51
• I would if I knew. I just had the tip to check out other protein types :)
– Dan
Commented Jul 10, 2019 at 16:37