Except for COD
liver oil, tuna and salmon there are very few dietary sources of Vit D, others being soy milk extract and organ meat
Sunlight is the best and sadly the only source for vegans
Next Steps
Yes as you rightly researched UV B is maximum in the middle of the day with efficient Vit D synthesis happening in just about 15 to 30 mins
Health Tips
Mind you this exposure should be direct and windows don't help or count here