My Mom has had both replaced, one last year and one 10 yrs ago. Evey surgery has its risks but if nothing unexpected occurs here is what to expect:
If a pre surgery PT session can be done, it is worth the time. Exercises to get the muscles into better shape prior to surgery means they will be better conditioned to recover after surgery. This goes for the whole body too.... the stronger going in, the stronger coming out. So exercising BOTH legs is important as one knee recovers the OTHER leg gets to do all the normal work. The arms get more of a work out too on the walker and for pushing up from chairs.
Surgery day... lots of waiting on your part. Lots of sleeping on his.
Post Op day 1 - dressings usually get changed by nursing, PT and OT (occupational therapy) evaluations. This will most likely include getting out of bed to the chair, the commode and even walking if everything goes well. Sometimes a person may only make it 10-15 feet to the bathroom with a walker but getting out of bed is the big thing.
IV meds usually get replaced by Pills. ICE THAT KNEE !!! My Mom's hospital offered cold sleeves that circulate ice water through a plastic sleeve that fit around the knee.... It did wonders for the pain. Don't let the pain get above a 3 on a 0-10 scale. If it hits 4... get meds or ice. There is no need to be a martyr with the pain and as long as the meds are tolerated, use them to the best advantage.
CPM (Continuous Passive Motion) machines may be ordered by the physician it moves the knee through bending and straightening while the person rest in bed. It also helps prevent swelling from occurring and the knee from becoming stiff. Not all places offer this.
Many times blood is given and hematocrit readings are taken way too early in the morning. Some hospitals will collect the blood from the surgery itself and use that to give back to the patient.
ANKLE PUMPS are an important exercise to do. There is a higher risk of blood clots forming after surgeries and it is better to prevent them than it is to try and dissolve them. Blood thinners are usually give 10-14 days after surgery to help prevent them as well.
Post Op day 2 - More PT to work on getting in/out of bed and learning how to do it without holding the leg. Exercises and more exercises.

Gadgets such as leg lifters can usually be purchased to help those first few days.
OT will want to see how well your husband can dress himself, can he get shoes on, get on/off the commode, in/out of the chair, tub, etc.
PT and OT is more of the same until the the patient is safe, and mobile. This will include stairs and even car transfers.
Post op day 3 - Most people are discharged on day 3 in this area. If it is done at a VA hospital the plan may be different. Patients can be discharged home, or to a rehab facility (many hospitals now have their own).
In this region, patients discharged home get home nursing to check the incision and home PT for continued mobility. Getting in and out of a hospital room can be very different from negotiating around the coffee table, cats and carpeted floors.
That will last for another 1-2 weeks until the patient is mobile enough to go to out patient PT. There... yup, more exercises, lots of stretching to regain the range of motion. Once the incision is healed massage of the area will help prevent scarring down and will improve the condition of the skin. More exercises.
Some modalities such as electrical stimulation which in conjunction with active muscle contractions will help regain strength sooner. More stretching, a stationary bike, more exercises....

ICE down after each session.
Once range is achieved that will go from fully straight to about 110-120 degrees of bending. PT will typically discharge with just an occasional follow up visit to the surgeon.
It is important that range is maintained. My Mom's first knee surgery was on her left leg and she did fine... six months later she climbed in the passengers seat of my compact car.... yeah, that knee didn't want to bend THAT far. LOL So she did a few exercises to remind the knee who was boss.
Most people who follow the Dr's and PT's instructions do very well. My MIL recently had hers done over the Easter holiday but staff is usually off or limited so she didn't get the PT that she should have the first 2-3 days. CPM machines are not the standard of care where she is at and after a week her motion became so limited that the surgeon had to manipulate her knee under anesthesia THEN ordered a CPM machine for her. NOT FUN! She lost a week's worth of recovery so her recovery was prolonged that much longer.
Side notes:
Six weeks after total knee replacements you can not tell the difference between those knees who have had the CPM and those who have not, so long term effectiveness is not significant. Short term effectiveness is the plan those first few weeks.
PT stands for Pain and Torture and OT is the OTHER torture.
It is going to hurt like **** but is well worth the outcome. Most all people are glad they had it done.
As with any surgery, a reputable surgeon and anesthetist are CRUCIAL. Ask around to see who else in your area has had a Total KNee Replacement and ask who, what, where, when and how questions.
Sorry this is so long but I hope the information helps.
Good luck to him.
Ceashels