I think this is from Vaj? Your guru gave you walking meditaiton? That is one of the things here in my path, referred to as open eye meditaiton and it can be all the time. If there are thoughts, having the mantra going along with taking one back to the present if they notice they are not there, helps to keep one in the present moment. If the mind is active with thoughts, either one can let them go on endlessly or replace those thoughts with thinking the mantra.
One who doesnt have a mantra can use Om, this is something my guru would give out to anyone. Further instructions for usefull practices can be seen on youtube under guruswamig Once doesnt have to be a disciple to do these practices and it is free to go there. I had already had clear experiences as a child. But with TM I would only transcend at most 4, 5 minutes absolute max. But once I had a clear awakening up to the heart, white hot completing the circuit with spontaneous mudras down the arms. Immediately thereafter I shot up to transcending 10 minutes or longer. Eventually I realized the only the thing that was blocking further progress was the subliminal idea I held somewhere that said I couldn't. As soon as it was realized that held-idea was empty of substantiality, impediments just dropped away and I could go up to 35 minutes max transcendent. If I maintain a steady practice I can go up to three hours now. If I'm not well rested, I have to take breaks and can't sustain the straight 2.5 - 3. Beyond that I began to work with, eyes open and going for hours, days or weeks. I do a lot of walking meditation now.
