Its half life in serum is a few minutes. But transport from injection site will take some time.
In the liver it is converted to IGF-1 that has a long half life.
Once receptors are saturated, more may not be efficient. So one could argue for two doses per day.
In a hormone replacement context, it is well known that the benefits do not become fully evident for 6 weeks. But the action on muscles may be immediate in terms of growth potential.