In the isekai genre of anime, it is a common trope for a person to be reborn into a baby's body while retaining their full cognitive abilities. Assuming they maintain full control of their coordination (balance and limb control), how long would it take for such a person to develop enough muscle strength to begin walking for a sustained period of at least a few minutes? With regular babies, the largest limiting factor is the amount of time it takes to learn to balance and walk, as far as I am aware.
While it would likely take some time for a person to recalibrate to their new body, for this question you can assume that time to be negligible. I am only asking after the stage of development/age at which their muscle strength would be sufficient.
How such a person would maintain their cognitive abilities while having the underdeveloped brain of a baby is not relevant. You can assume that to be magic.