We will be traveling to the big island at the end of April. We will have 5 full days. On the 6th day our flight leaves for home at 9:00 PM. A rental car is included in our visit, and we're booked at the Waikoloa Beach Marriott. We know that we want to visit Volcanoes National Park and Hilo. We also are planning on a helicopter ride to view the volcanoes and waterfalls. We are in our 60's and will not be able to snorkel or hike very much. We do, however, like to get on the water via boat. We love craft beer, bar food and enjoy sampling local cuisine. My problem is that I really have no idea how to schedule the visit or what restaurants would be good to take in. I'm not sure which day(s) would be best to visit the National Park or what day(s) would be best to visit Hilo. Can anyone offer us some advice?

The only advice I can give you is to go to the LavaLava Beach Club (basically next door to the Marriott) for drinks (and food if you wish) at sunset. Try to snag a seat on the beach. Very casual and fun, drinks are good, sunset is spectacular.

VNP and Hilo are large areas, so day of week really doesn't matter (if that was your question).

The best helicopter tour can't be predicted, since it depends on how (or even if) lava is flowing when you visit. In general, lava flows not above ground, but in underground tunnels, and it's invisible from the air during the day due to bright sunlight. So if the goal is to see active lava, evening tours are preferable if your operator offers them.

For food, restaurants at Kohala resort areas including the Marriott tend to be pricey. More budget-friendly alternatives exist in both Waimea and Kailua-Kona, staying in Waikoloa you'll be much closer to the first of those two. Highly recommend Merriman's in Waimea for dinner.

There currently are "Scattered surface lava flows" but you'd have to ask whether a company will fly over them (and I have to say that we went in broad daylight and saw red flowing lava; it was amazing). http://hvo.wr.usgs.gov/activity/kilaueastatus.php

The LavaLava sunset is the same as from the Waikoloa grounds and beach. Sit in a beach chair or wander down the beach (past the crowds at LavaLava)and enjoy! (We bring our own bev. of choice.)

The harbor restaurants of Kawaihae to the north are very good, and less pricey than the resorts: Blue Dragon, Cafe Pesto, Plantation Grill are all very good, IMO (and especially lunch at the Da Fish House truck).https://www.tripadvisor.com/Restaura...ii_Hawaii.html
There's also a food court at the Queens Shops (next door to the Marriott) if you just want cheap/fast, and a couple of chains and casual food there and at Kings Shops across the street.

If you don't mind missing a night of paid lodging, you could catch your copter ride from Hilo in the a.m. (1.5 hours drive from Marriott via Daniel K. Inouye Highway, or Saddle road), then explore Volcano NP the rest of the day, and stay over in Volcano village (or the campground cabins in Volcano if they're open again) to view the glow of the crater at night (and explore Hilo before driving back to Waikoloa).

FWIW, we enjoyed Pueo's much more than we liked Café Pesto (which was okay, but I wouldn't go out of my way).

Out of curiosity, have you ever snorkeled before? I certainly don't want to presume anything about your health or stamina, but from my experience, it's not particularly arduous if the water conditions are favorable. The snorkeling on the Big Island is fantastic, so if you have any interest in it, I'd encourage you to give it further thought. There are several operators that can take you out to one or several good spots. My experience was with Sea Quest (out of Kona). We had a fantastic time; one of my best days ever.

Agree absolutely: you could even just enter from a variety of beaches near the Waikoloa Resort area.

Sea Quest was a good trip; we went to Kealakekua Bay (Capt. Cook) and "Two Step" (Honaunau Bay), and it was easy entry/exit and beautiful snorkeling.
There are several boat tours (large and small) out of Kona and Keauhou Bay, and even from Kawaihae harbor, which would be closest, after A-Bay at the Marriott. Ocean Sports has one from A-Bay for $150, but you can do one from ~$75 with coupons.

Here's some info from VNP's website on current volcanic activity. Note that of the two locations where the volcano continues to erupt, only one is accessible to the public. And that is best viewed at night from the Jaggar Museum. But it's generally not advisable to drive across the island in the dark, so you might consider (double) booking a night in Volcano, which would allow you to drive the Hamakua Coast and visit Hilo on the way to VNP. Then after finishing your VNP visit the following morning drive a different route back to Waikoloa. Checks your Hilo and VNP boxes with minimal drive drive time.

We've been on the water a few times with Mauna Lani Sea Adventures and enjoyed each trip. Our favorite was paddling an outrigger with Uncle Gary who operates out of the Beach Center: http://maunalaniseaadventures.com/. We plan to do the same excursion when we're on island in a couple months (and we're about your age).

+ 1 for Da Fish House. We've also enjoyed several others that have been recommended here, but our go-to place is Napua, situated just above the beach at Makaiwa Bay in the Mauna Lani Resort property. Best craft brews we've found are at Big Island Brewhaus in Waimea.

I'm wondering the same thing as indyhiker about snorkeling; try it (if you haven't), you'll like it. You'd also enjoy a drive north to Hawi, Kapa'au, Pololu Valley overlook, and possibly the short hike into the valley. Do the trip as a loop, taking hwy 250 to/from Waimea one direction and hwy 270 along the coast the other. Lot of interesting historical parks and sites along the loop.