From my understanding it can actually take anything up to 6 weeks before all the LP test results come through when they are looking into MS.
What is more typical seems to change depending on your country, in mine you usually have to wait until your scheduled follow up appointment or sooner if you get a call to come in to see the neurologist earlier than scheduled but in the US everyone seems to get access to their test results long before their follow up appointment with the neurologist or Dr who ordered the tests done.
Most dr's prefer to discuss a patients test results face to face, usually at their previously scheduled follow up appointment, or at an appointment that is organised only after all that patients different test results have come in, so it is quite likely that you will have to wait to find out the meaning of your results until your next appointment with your neuro.
Keep in mind that 'wait and see' is typical with a neurological condition like MS and unlike other medical fields, neurologists typically work in long time blocks and usually see patients every 3 months, 4 months, 6 months, 12 months, 24 months. Also i don't know if it will help you to know or not but it's not uncommon for officially diagnosed MSer's to have to go through the diagnostic processes all over again if they've needed to see a different neurologist than the one that diagnosed them with MS...
Hope that helps......JJ
btw your LP results don't have anything to do with when you have an MRI