I walked from Sepulveda to TBIT on the Sunday after thanksgiving when the horseshoe was gridlocked. Took 9 minutes but I walk kind of fast.

TBIT to T7 is reverse direction and slightly shorter distance than Sepulveda to TBIT so most people can do it in 10 minutes at moderately fast pace.

Agree it's not worth waiting for the land side bus... unless you catch it right when you exit TBIT.