I am confused. Hydraulic cement is a cement that reacts with water, which includes many different cements, but excludes epoxies, and similar. If we are talking the plug products, those are designed to be pushed into a crack with water coming through and react fast enough to plug the leak. If we are talking Portland cement, it is usually used with some type of filler, like sand for mortar or grout, or sand and stone for concrete. Portland cement in any of its forms takes upwards of an hour without retarders to become unworkable, if it is being mixed periodically.
For the patching you are trying to do, I don't see the use of a plug product as being needed or even desired, do to the rapid set characteristics. Many of the grouts are too fluid to use, though the water addition could be held back to keep the product stiff. Any of the mortars would work fine to fill the space.
Zone 7 A/B
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Richard