William the Conqueror certainly did not delay the launch of his fleet in anticipation of the potential invasion of the Norwegians under Harald Hardrada. It is true that the Norman fleet delayed its launch, however, to quote the venerable David C. Douglas:

"The uncertain factor was the Channel wind. Duke William was himself fully conscious of this, and contemporary writers describe his supplications for a chance in the weather, and picture him during these fateful days as constantly gazing towards the vane on the church tower of os Saint-Valery." (William the Conqueror, p. 194)

Indeed, the Conqueror almost certainly expected the English to resist his landing at Pevensey on September 28, 1066, and planned accordingly. Wace records that:

"The archers disembarked first and reached land first, at which time each of them stretched his bow, with their quivers hanging at their sides. They were all shaven and tonsured and all dressed in short garments, ready to attack and ready to flee, ready to turn and ready to escape; they all traveled the length of the shore and found no armed man there. When the archers disembarked, the knights then did so, all armed and wearing hauberks, with their shields around their necks and their helmets laced on. They came ashore together, each armed and on horseback, all with their swords girt about them; they reached open land with their lances raised. The barons had banners and the knights had pennons; they stationed themselves next to the archers, having first taken possession of the terrain." (The History of the Norman People: Wace's Roman de Rou, p. 163)

According to Bernard Bachrach, the passage above “conforms to a textbook model for securing a position in a potentially dangerous situation." ("On the Origins of William the Conqueror's Horse Transports," p. 512) If Wace can be believed, this represents unequivocal evidence that William’s army, including the crucial mounted contingent, landed in battle-ready condition, underlining the fact that the Conqueror expected armed opposition to his landing. If he had anticipated the Norwegians to weaken the English as much as OPs question suggests, the Norman landing would not have been accomplished a thoroughly as it was.

Also to consider is the fact that it was extraordinarily expensive to keep a large army in one place for an extended amount of time, as the Conqueror was doing in 1066. In his famous article, “The Military Administration of the Norman Conquest,” Bachrach estimates a conservative lower limit for the total of the Conqueror’s expeditionary force at around 10,000 effectives and 4,000 in ship crewmen and other noncombatants. The 10,000 effectives also includes 2,000 to 3,000 cavalrymen and their horses, which would have been extremely expensive to provide for. And provide for his army William did, as he forbade plunder of his own lands during the stay in Normandy. Any increase in the stay would have increased the financial and logistical stress Duke William was already under, and he would have wanted to depart for England as quickly as possible.

Thus, William was did not extend his stay in Normandy in anticipation of the Norwegian invasion of Harald Hardrada, but for the much more mundane purpose of unfavorable weather conditions.

Sources:

"William the Conqueror," by David C. Douglas.

"On the Origins of William the Conqueror's Horse Transports," by Bernard Bachrach.

“The Military Administration of the Norman Conquest,” by Bernard Bachrach.

"The History of the Norman People: Wace's Roman de Rou," by Wace.

edit: I know some people don't love this sort of thing, but I'm happily surprised to be gilded. It's never happened before so thanks!

I just finished reading David Howarth's 1066: The Year Of The Conquest, and he indicates that William didn't have a clue. According to Howarth, the delay that William experienced was entirely due to weather, i.e. waiting for the right wind to blow so he could sail to England.

Harald Hardrada was brought to England by King Harold's brother, Tostig, in an attempt to reclaim his earldom (which he had been force-ably removed from because the people in the earldom didn't like him).

Unfortunately, that meant that King Harold -- who had been guarding the coast waiting for William all summer -- had to take his army North, where he resoundingly beat Tostig and Harald Hardrada. Unfortunately, just a day or two after that victory, messengers arrived informing him that William had landed.

Not to get too deep, but William had the Pope's blessing (Howarth says obtained via trickery), and rode into battle with the Papal banner overhead. That combined with pretty much every other bit of luck going against him convinced King Harold that God's judgement was against him. As such, it appears (again, according to Howarth) that King Harold was a morally broken man when he faced William, and thus squandered many chances to repel the invaders.

This is an excellent question. As a follow up, what were the relationship between the Normans and the Scandinavians at this time, considering their common ancestry?

21 upvotes to 1066 come on guys