IND Timeline The limit of the timescale for the FDA to come back to the Company on the Clinical Hold Response is very clear (see below) - this is presumably why they have confidence in mid-May:
'The IND application sponsor is expected to address the cited deficiencies in writing and submit a complete response to the issue(s) identified in the clinical hold letter in a separate submission. Once the complete response to all of the clinical hold deficiencies has been received, FDA will review the submission within 30 calendar days and determine whether the applicant’s response to clinical hold satisfactorily addresses the issues. The investigation may resume after FDA (usually the Division Director or their designee) has notified the applicant that the investigation may proceed.'