As someone that served on a federal grand jury, no. Well, at least not vocally, I presume people internally weren't basing their votes on pop culture but saying something else out loud. Then again the strength of most cases that make it to the grand jury, from what I saw, are fairly strong, and the burden of proof is lower (since indictment != conviction). If the case is weak the ADA's wouldn't even bring it to us.
Perhaps I wasn't clear: gambits by the DA or defense based on timing of world / cultural events (beyond holidays, weekends and lunch) to garner a favorable state-of-mind of adjudicators.
There is, iirc, also a time limit between when an investigation begins and one an indictment is filed. The idea being to prevent the government from simply having someone under investigation in perpetuity. I suppose the ADAs COULD try and time the indictment against unrelated pop-culture events, but in my experience it seems so unlikely as to be mostly the stuff of movies. Delays more frequently where due to problems getting financial records or untangling complex webs of them, problems locating willing witnesses, problems with witness intimidation, etc..
