You should continue to take it at night!

LDN has virtually no side effects. Occasionally, during the first week's use of LDN, patients may complain of some difficulty sleeping. This rarely persists after the first week. Should it do so, dosage can be reduced from 4.5mg to 3mg nightly.

What is the best dosage of LDN to begin treatment with?
For an adult who is not significantly below the normal weight range, the optimal dose of LDN is 4.5mg, taken each night at bedtime; i.e., between 9pm and 3am. One can begin at this dose level. If one were to develop persistent sleep disturbance (i.e., a sleep disturbance lasting longer than 10 to 14 days) after starting LDN, which occurs in less than 2% of users, then the dose may be decreased to 3mg or 2mg.
People who have multiple sclerosis that has led to muscle spasms are advised to begin treatment with just 3mg daily and to maintain that dosage.

If I have to work on a night shift, for example from midnight to 8a.m., at what time should I take my LDN?
Continue to take LDN as recommended above; i.e., between 9pm and 3am. This relates to the fact that the endorphins for each day are always produced in the pre-dawn hours, regardless of the hours when one is awake or sleeping.

all the above information is taken from www.lowdosenaltrexone.org