It depends on the aim of your study. For example, for some structures with special conditions, we need to know early-age concrete properties. However, if you want to publish a paper, it is better to cover all concrete ages.
It is worth mentioning that the "procedure of curing for freeze-thaw cycle test" is way more important than the concrete ages. As you know, you can find the proper procedure on ASTM C666 or ASHTTO T 161 standards.
Hello, it all depends on the type of cmenet you want to use. J follows the guidelines that are applied in this matter to road concrete in Poland, and so for CEM I - 28 days, for CEM II - 56 days and for CEM III - 90 days.
Test cubes with dimensions 15 x 15 x 15 cm.For more details see standards EN 12390-9: 2006 (Testing hardened concrete-part9: freeze-Thaw-resistance-scaling) or ASTM C 666-2008