Depends on a lot of things, like individual tolerance and route of administration. Were you planning on smoking it or taking it orally? Smoking kicks in faster, but the high isn't nearly as strong. A book called The Chinese Encounter with Opium puts the ratio at 20 parts smoked to one part taken orally, and that sounds about right, based on my experience. In the old days, opium eaters were considered the real addicts. Switching from smoking to eating indicated the progression of a person's addiction to a socially unacceptable level.
You may find opium weak if you have experience with other opiates. If you're opiate naive, you may be able to catch a decent nod on it, but that doesn't last. It doesn't matter how many tolerance breaks you take, it will never be the same as the first few times. As a one-off, it may be "worth it" for you, but a habit probably won't be unless you seriously need to self-medicate.