@farmboy
I think you're really asking when you can expect the Effexor to be at a steady state.

Pfizer (mfr of Effexor) says of Effexor XR, "Dose increases should be in increments of up to 75 mg per day, as needed, and should be made at intervals of not less than 4 days, since steady-state plasma levels of venlafaxine and its major metabolites are achieved in most patients by day 4."

https://www.rxlist.com/effexor-xr-drug.htm#clinpharm--
"Steady-state concentrations of venlafaxine and ODV (its major active metabolite) in plasma are attained within 3 days of oral multiple-dose therapy. ...When equal daily doses of venlafaxine were administered as either an immediate-release tablet, or the extended-release capsule, the exposure to both venlafaxine and ODV was similar for the two treatments, and the fluctuation in plasma concentrations was slightly lower with the Effexor XR capsule. Therefore, Effexor XR provides a slower rate of absorption, but the same extent of absorption compared with the immediate-release tablet."

https://www.mayoclinicproceedings.org/article/S0025-6196(11)62919-4/pdf--
"The ideal antidepressant should have a half-life consistent with once-a-day dosing or a half-life of about 24 hours. The shorter half-life drug reaches steady state sooner than the longer half-life compound and also is eliminated quicker.

A pharmacokinetic rule of thumb is that it takes about 4 to 5 times the elimination half-life with a constant dosing interval to achieve steady-state levels. With a drug that has a half-life of 1 day, this steady state is reached after 4 to 5 days. For a drug with the elimination half-life of 4 days, the time to steady state with once-a-day dosing is 16 to 20 days.

Additionally, the phenomenon of cumulation, or accumulation occurs when a drug is given at an interval shorter than 4 to 5 times its half-life. In this case, the blood level at steady state is much higher than that after the first dose. This is because the drug is given at an interval that is shorter than the time necessary for the body to eliminate most of the previous dose.

Another pharmacokinetic rule of thumb based on the elimination half-life is that it takes about 4 to 5 times the elimination half-life to have more than 90% of the drug eliminated from the body after the medication is discontinued. Thus, a drug with an intermediate half-life shortens the time to steady state and shortens the time for elimination.

This knowledge is important when therapy is initiated, when dosages are adjusted, when a medication is discontinued because of an adverse effect, or when one drug is discontinued before another drug is initiated that might cause a drug interaction.

From a theoretical standpoint, the compounds with a half-life between about 17 and 36 hours can be given once per day to maintain good steady-state levels. Drugs with lesser half-lives must be given more frequently, and those with greater half-lives can be given less often than once per day, although this approach is generally not used. ...An extended-release form of venlafaxine allows once-daily dosing."