Using this field you can set how many frames of “correct” time code Cubase VST should receive before attempting “lock” (synchronize) to incoming time code. If you have a tape recorder with a very short start-up time, you could try lowering this number to make lock-up even faster than it already is. If you have Chase Events turned on, and many Events to chase, you could try raising this number.
On a tape with time code (SMPTE) dropouts may occur. If a drop-out is very long, Cubase VST may (temporarily) stop. In the Dropout Time field you can set how long a drop-out (in frames) should be tolerated until Cubase VST decides that the tape isn't good enough to synchronize to. If you have a very stable time code source, you may lower this number to make Cubase VST stop more swiftly after the tape recorder has been stopped.