Strength gains can be compromised due to concurrent training (when pairing endurance and strength training together, one right after the other). As your body is trying to adapt to both forms of exercise. This is not possible because adaptations to endurance training are often inconsistent with adaptations observed during strength training.
If you want to perform endurance training, know that both high-intensity interval training and moderate-intensity aerobic exercise elicits the interference effect to roughly the same degree.
It is advised cardio be performed at times that are not concurrent with strength training, which would be the best option for minimizing the interference effect.
If you find yourself with the time or feel the need to include an extra training session in your week I recommend you use this session to focus on weak points. I suggest you pick 2-3 exercises that target muscles that you feel are weaker areas. Concentrate on working these areas at a higher rep range of (12-15).
When doing so, try to factor it in so that you are not training the same muscle group on consecutive days, as this will lead to sub-optimal performance. Also note that the larger muscles such as quads, pecs, and glutes may take up to 3 days to recover so training them more than 2 days per week may be difficult to map out.
But the smaller muscle like the biceps, medial and rear delts, and calves do not need as long to recover as their growth curves occur every 1 or 2 days so these can be trained more frequently.
Rest periods with compound exercises (multi-joint) are longer than the isolation exercises as you will require more time to recover from them. If you feel you require a little longer than the 2 mins stipulated in order to optimize performance then take it.
This should be less of a concern with isolation exercises (single joint), which have shorter rest times attributed to them as there is not such a demand on the body, try and be regimented with these rest periods but if you feel that reps could be compromised by executing the next set before you are ready then take extra time.