That is a bad reason, yes. However, the prosecutor also objected to Levison's proposal to supply metadata, where he would wait until the 60 days were up, decryp

That is a bad reason, yes. However, the prosecutor also objected to Levison's proposal to supply metadata, where he would wait until the 60 days were up, decrypt the stored messages (from which, to my knowledge, he could only read the headers unencrypted - the body is encrypted with PGP, I think), strip the "Subject" headers (per the legal standards on pen/trap orders) and then deliver that data to the FBI, via SCP, in bulk. One reason that this was rejected, then, was that it did not fulfill the requirements of the 'trap/trace' part of the order, which require the metadata to be provided in real time or close to real time.