I don't think they block based on big transfer to trust solely. Think they block based on the amount too. I use posb block transfer to CIMB only auto release 24 hrs later.
Another reader say nowadays he do 1 day earlier but this can be tricky as CIMB look at last day of month vs comparison month last day.
so in my case a $49k from dbs went through and fro with trust without issues- but this was an account that has transfers experience with trust account .
Tried varying amounts from uob and citibank ($40k - $100k) ; these were blocked.
For CIMB, similar problems.
Overcame those in CIMB, by limiting total account to $50k otherwise 50% withdrawal would trigger.
Deposits into CIMB limited to $19k to prevent 24 hours hold.