Quite so. There's also a mention of a two-minute limit on that. But it's completely incompatible with what we see in "Encounter at Farpoint", which is the saucer maintaining pretty high warp so that it can evenly compete with the battle section on the final leg of the trip to Deneb IV.
Timo Saloniemi
For what it's worth, the wide angle shot from Farpoint shows both the saucer and stardrive at sublight immediately after separation. Then the next time we see the stardrive it's back at warp.