So what is Beard Oil? "Beard oil is hydrating to the skin and helps soften and tame beard hair, which means it also does double-duty as a styling agent. According to Schneidman, the ideal beard should look shiny and groomed -- not dusty, flaky and shaggy." Source
Beard oil is pretty essential in everyday grooming of your beard. However it's fairly opinionated as to when you should use it. Some say beard oil can be used as a styling agent, others just use it for moisturizing purposes. That being said I'll give you my current regiment I use in taking care of my beard.
Beard Wax - Morning AM (Must have had beard oil/balm in the night before)
Mustache Wax - Morning AM (Only use on mustache, as this is a heavier duty wax)
Beard Balm / Beard Oil - Evening PM (After face wash)
These are the typical times I will use the products. It's really just up to you though. If you typically take more showers in the morning, then putting on beard oil/balm in the morning will work too. However I typically find that when I was doing this, I would have more excess crazyiness about my beard because I didn't tame it more with beard wax. It's up to you, and your routine!
What I'm going to do is link a few good pages on how to make beard oil, this is a very inexpensive alternative to buying some of the more expensive brands on the internet.
Manly Essential Beard Oil
Art of Manliness DIY Beard Oil
10 DIY Beard Oil Recipes
Comment with any questions, or concerns!