Is it possible to use a hot water recirculation pump with a PEX home run system?
There are two issues to the time needed for hot water; one: the home run from the manifold to the faucet and two: the feed line from the hot water heater through the manifold. The key is to know how much cold water is sitting in the lines and the flow rate of your faucet. You can do a search for "PEX specifications" to get the volume of water in the lines. The volume of water is based on inside diameter and length so is applicable to any pipe that is measured by inside diameter, not just PEX. You can time how long it takes to fill a container, like a 2 quart measuring cup to calculate your flow rate.

1/2" PEX holds .92 gallons per 100'. On a relatively short 25' run, that's .23 gallons, on a relatively long 50' run, that's .46 gallons. With a 1.5 gal. per minute faucet, thats almost 10 seconds for the 25' run and 20 seconds for the 50' run. But wait, there's more! Look at that 12' of 3/4" line from the water heater to the manifold. And also consider the more that 1' run through the hot side of the manifold which can be as large as 1 1/4" inside diameter. Because of the larger diameters, that's another .25 gallons. You've added another 10 seconds. Now you have 20 seconds for the 25' run and 30 seconds for the 50' run.

The most effective and expensive option is to place the line that you most want fast hot water to at the far end of the manifold and recirculate only that one. It now has almost instant hot water and everywhere else has it 10 seconds sooner because the water in the manifold is now hot.

A less effective but probably much cheaper alternative is to move the last hot line off the manifold to a tee above the manifold like the other one shown there. That frees up the end port to use for recirculating. No sink has instant hot water but this cuts 10 seconds off wait times at all locations and is simple to plumb and insulate.

The absolute cheapest would be if the plumber had set the water heater a couple feet over and used the code minumum 18" connector between the water heater and the manifold. That would have cut out 10 1/2' of 3/4" pipe and would have reduced the wait time at all locations by about 7 seconds. It could still be done but, since the manifold would have to be turned over so that the feeds are on the bottom, which also reverses which side the hot lines are on, it would be time comsuming. 

Note that this example used a typical 1.5 gal/min lavatory faucet. A 2.0 gal/min kitchen faucet would take less time. If you have a 1.0 or 1.2 gal/min low flow faucet, the wait is longer. If you have an ultra low flow 0.5 gal/min faucet, make a sandwich or read a book while you wait.