I was tickled to see the Jackboots! That is a classic sign the troops are "early war" and quite possibly very early! Just how early depends on other factors. If you can see the tunic details, and the pockets have scalloped flaps and pleats, you should be good through 1941. Still have scalloped pocket flaps, but the pleats are gone? You are good for 1942. Scalloped pocket flaps are gone? Now you are likely in 1943.
In photos, helmets are not much use in determining the period. Those national colors and eagle shield decals on the sides were present from the start, and initially the helmets were painted a semi-gloss color, but starting in late March 1940 the national colors shield was discontinued on army helmets. And the helmets were to be painted a matte color rather than semi-gloss. This did NOT mean that every helmet had that decal painted over before April of that year. So if you want your troops to have the double-decal for France 1940, you are fine. The factory stopped applying the decals, and the old decals were to be scrapped off or painted over. But not every soldier complied. You can easily find photos in mid and late war of German soldiers with national decals still on their helmets.
The Luftwaffe received a similar order in June 1940 regarding the national shield decal. The SS received their orders to remove or paint over the national shield from their helmets in August 1940.
In August 1943 the eagle shield was discontinued. Yet again, you can find photos of late war troops with eagle decals still on their helmets.
