Skipping a dose will not cause any long term problems.
When you take any drug, as soon as absorption is complete, which is from a few minutes to an hour or so, your blood level will be at the highest. We call this a peak blood level. As the day goes on,our bodies slowly eliminate the absorbed drug at a rate known as the "elimination half-life". That is, every drug has a time period where one-half of the drug is eliminated from the body. For example, if a drug has an elimination half-life of 4 hours, then 4 hours after the peak blood level, you will have 50% of that peak blood level, and in another 4 hours, you will be at 75%, then 87.5%, then 93.75%, and 97% and so on, if you do not take another dose. After 5 half-lives, the drug is essentially gone from the body and only trace amounts would be detectable, but not effective. If you are taking your drugs on a schedule, the lowest blood level will be just before your next dose. This is called the valley. All drugs have peaks and valleys. Even timed release or extended release drugs have peaks and valleys, but the difference between the peak and valley is not as great as any drug product that is not timed or extended release.
If you are going to have a blood level taken to determine your proper dose, then you should have the blood sample collected from your body at the valley, not the peak or some where in between.
Missing one dose, in the long run, is not going to affect you overall progress in achieving your final goal. HRT takes years to see full development. The important thing to remember is just keep taking your meds and let you doctor determine your dose that will keep you somewhere in the female range. The exact blood level is not critical.
