So...that'd be early April or so, if I'm not mistaken. I'm not Jewish, so maybe one of our other members could doublecheck this goyim's memory.
Are you saying that everything else would stay the same? Like that Syria and Egypt would launch it in 1973? That'd make a difference. If they launched in April of 1973 that'd be earlier and the SAM system over the Sinai might not be in place as completely as it was by October. Though it's hard to imagine just how many SAM-2s, -3s, and -6s got shipped in during four or five month window that would be openned up.
In actuality, it might work better for the Egyptians and Syrians. Like you pointed out, the roads were clear when the Arabs invaded. Not only that, but just about every civilian in the country was at home and there were detailed plans in place to call up the reservists in just this event.
For those that are unfamiliar with the problems that they faced with the Yom Kippur War reservist call-up, apparently Jews were at home specifically not listening to the radio or answering the phone. According to Simon Dunstan's The Yom Kippur War, military couriers were assigned to do the job in the event of a Yom Kippur call-up.
The Israelis might very well see some of the reserve divisions go into the line 24 or even 36 hours later. This is almost what the Syrians were planning on in 1973. Abraham Rabinowitz's book on the war cites interviews with POWs that said they didn't expect Israeli reserve units to get to the field in force (read: brigade-sized) until the second or third day. In OTL, they were facing reserves in bits and pieces since almost the very beginning: the 2 Centurions of Task Force Zvika along the Tapline basically blunted a mechanized brigade on their own and when division armed with Shermans arrived on the north bank of the Jordan by Day 2 the Syrians were shocked.