[mdjlucan]

 I sprayed the weeds yesterday morning if it rains tomorrow  Will the weed killer still work or not

[8doubles]

It should be ok .
Once the killer has had time to dry on the plant enough should have been absorbed to do the job.

[mdjlucan]

O k thanks

[Yorkie]

Yes, it should be fine.  The instructions often say it should be dry for 6 hours after application.