Yes, candidates can take a recertification exam on or before their certification expiration date. So if your CCNA R&S certification expiration date is April 19, 2018, you can still take an exam on that date (subject to availability) or before that. If you pass, you will be recertified for 3 years.
Also, as Daniel mentioned, the processing of exam results and posting into your Certification Tracking System profile is normally fast in most situations. However, even if there is some delay in the posting of the exam results into your profile, you will be good for recertification as long as the exam was passed on or before your certification expiration date.
For example, if you pass a CCNP exam on April 19th (your expiration date) there is a chance that the exam results will post in your profile after that date. You will still qualify to be recertified because you passed the exam on the expiration date, which is what counts. If for some reason the recertification status does not update automatically, it can be corrected by opening a case with the Certification & Communities Online Support team and attaching a copy of your exam score report.
I hope this helps and good luck!
Cisco Learning Network Moderator