I'd like to run some AC/Noise simulation but in my design I have clocked latches that required a few micro-sec to set the circuit in the proper configuration.
How to run the AC simu from a point established after a tran?
Well, pick a point, set it in transient options (if you use cadence), configure transient and ac or noise and then run.
However, since you have clocked latches, maybe a better option for you would be to run PNOISE.
AC analysis bias point is set in initial transient solution. If the intended setpoint isn't achieved automatically, you can use .IC command to set node voltages and branch currents as required.