This depends on the speed of your computer and on the nature of the MIDI destination to which you are patching thru.

The "Use CoreMIDI Patch Thru" option in Digital Performer 4.5 & later relies on Mac OS X CoreMIDI enhancements that were introduced in Mac OS X v10.3. This option, found under MIDI Solo & Patch Thru in DP's Preferences, is grayed out if you are running Mac OS X v10.2.

Also, if the MIDI tracking you are patching thru has realtime MIDI effects on it, CoreMIDI Patch Thru will not be used, even if it is checked in your preferences. To use CoreMIDI patch thru, record-enable a MIDI track without realtime effects on it.

Note: As of Digital Performer 6.01 and later, the CoreMIDI Patch Thru functionality has been absorbed into DP's other Patch Thru abilities. The CoreMIDI Patch Thru preference, previously found under Preferences > MIDI Solo & Patch Thru, has been removed.