Depends. If you already have some gyno for any reason then I wouldn't. Also if you are not on an Aromatase inhibitor (AI) I wouldn't and IMO even though I have done this, you are better off saving it. I doubt you know how to control estro well enough.
You aren't going to gain much more, may add a lot of water, will increase quite a bit and at that time its not good to have excess estrogen. It's mentally bad for a lot of people because they put on some water weight fast, then come off and immediately lose 10lbs and are just stopping test. It leaves most with a defeated feeling. Also it will raise estro, that's how it works, and you don't want elevated estro at a time that T is clearing. That typically results in gyno, and more of a crash because t is clearing and estro is elevated, you start to feel like a woman. Lol.
If you had more experience, knew how much of an Aromatase inhibitor (AI) you need on certain cycles, with test and dbol, how much you need in post cycle therapy (pct), etc. then it would be different. You can do what you want but I'm willing to bet at this point, 4-5 weeks worth of some mass, some water, extra estro, are not worth it in the end.
If you decide you are going to do it, I would do 30mg a day. But this all depends on your age, bf, etc because it will make a difference in the amount of aromatization. If you plan to add Human Chorionic Gonadotropin (HCG) prior to post cycle therapy (pct), that will increase estro as well, along with increasing t levels, but you haven't made it thru one cycle or post cycle therapy (pct) yet, I'm assuming it's your first cycle, so I would see how you do with that first.
In general it's not the best idea to use highly aromatizing compounds at theend of a cycle, that's not saying it can't or shouldn't be done, and not saying it can't be beneficial and add some decent size near the end. Personally I would do something like that on a longer cycle, maybe starting week 15-16 of a 20 week cycle to give yourself a nice boost, especially if you have reached a sticking point but again depends on the person because some lose their appetite, feel sluggish, have back pumps, others feel pretty good.
I say get the dbol from your friend and hold on to it.