Not to Soak:

Do not soak lifters that are pre-oiled, pre-assembled, or labeled “no pre-soak required” by the manufacturer. Many modern hydraulic lifters are shipped with "wet" assembly oil and are manufactured with precise internal clearances, and soaking can actually cause them to over-pump. Over-filled lifters may hold valves off the seat during initial startup, leading to misfires, low compression, hard starting or camshaft failures.  Many cam manufacturers do not offer warranty consideration for improper installation.

To Soak:

Soaking hydraulic lifters in clean engine oil before installation is recommended only when the lifters are shipped dry. Pre-soaking in this case allows oil to fill the internal reservoir, reducing the chance of dry  startup noise and helping the lifter pump up more quickly on initial fire-up. Always allow the lifter to be filled by using an engine pre-priming method, no pumping.

If the lifter manufacturer provides specific instructions, always follow them. Lifter installation instructions are  easily found on line and can be requested from the manufacturer.  Break in springs are recommended for high performance camshafts. Ensure that you oil the lifter body and roller or foot, apply a quality break in assembly  lube where required, and rely on proper priming of the oiling system before startup rather than soaking. A high zinc/phosphorous content break in oil is required.