I will say sooner rather than later. The plant is expending energy for the grapes, rather than the vine. The sooner you eliminate them the energy can revert to vine production. This year you are developing the vine above ground, and the roots below ground. What you see above ground mirrors root development below ground. As much foliage as you see, that is how much roots you now have. Don't do any pruning this summer. Next spring you will prune to 2-3 buds and experience explosive growth next year, and next year you will develop the permanent trunk and the cordons. Each vine should have a bamboo stake presently. The stake is a guide to bring the vine to your fruiting wire safely As the vine emerges from the protector tie it to the stake with surveyors tape. Otherwise they may snap off in the wind.