When should I start to do workouts?

I would recommend to first incorporate a long run (my favorite run of the week), to build more aerobic capacity, and thus more capacity for better workouts. As you already know, they are 60-90 minutes in length usually, so go out conservatively! Perhaps start at 65 ish minutes for a bit since your longest runs (according to the post) are 50 ish minutes.

After you get settled into that (or at the same time), add tempos once more into your routine. I think that would be a few weeks from incorporation of the long run. Just remember to be careful about these (they will certainly be faster than runs right now). Of course, 30-45 minutes of aerobic threshold pace.

Next, add in strides to the latter portion of recovery runs. This will make the transition into speedwork less dangerous. 4-6x100m is a reliable amount. Add these in whenever you feel is right.

Finally, you can start the track intervals. Once again, I cannot predict how you will be feeling by then, but I estimate it will take another couple weeks from adding in tempos to beginning track workouts. Start with 200 meter repeats, as these are usually pretty light for a distance runner such as yourself. You'll get back into it soon enough.

Remember, you will get back into it whenever you feel like it is right, this is not a definitive timeline, just a suggestion. You will know what is best to do when you get there, however I hope this helps!

In short, you can start workouts immediately

Since it sounds like you are injury prone and coming off a long layoff, start with one hard effort per week. And keep it unstructured. A progression run or a fartlek. Maybe a normal 6 mile run run as 2mi easy, 2 mi moderate, 2 mi hard. Or a fartlek where within a 4-8 mile run you break into several surges to a lightpole or a tree you pick out. Then jog until you catch your breathe and repeat that a bunch of times.

After a few weeks, start to add structure. 3-4 mile tempo runs at a good clip or 6-10 mile progression runs starting easy and cutting down. Add strides or 30 second buildups at quick speed with ample

recovery to find some leg speed. Eventually you’ll pick out a race and begin to tailor your training to that and get more specific

I do not think it is the aerobic capacity that stops us, but rather the muscular readiness. Workouts and especially short interval work is very efficient at getting back to a basic endurance levels, but the musclular strenght might be off to endure faster running and long running. So I would just progress with short work and if you have to do very slowly progression I would start with strides and easy hill workouts (like 45-60s and jog down), but rather than one "big" workout, I would do several (like 2) shorter ones into easy runs through the week. The muscles can then get used to the work. I would as quickly as possible get into hill sprints after som weeks of strides and easy hill repeats. Progress from 3x10s "easy" once a week, to 3x10s 95% and then progress over weeks up to 8x10s once per week or to 5x10s two times a week.

But the really good leg feel for me came when I started with heavy strength the the legs. Like deadlift, squats and calf raises. Just progress those over 4 weeks if you start with it.

Then I would have progressed into a threshold workout and a 15x40s hill workout with hill sprints and strides elsewhere in the week. When that works including a longer run once a week, I would not be afraid of doing other faster workouts.