Nobody at the SJ Ranger station will give you any information about the trail below Long Valley (that's the first 10 miles or so of the trail, and the first 8,000 feet of elevation gain). That part is called the Skyline Trail, and it is not considered an official trail by any agency.
In March, the traverse from Grubb's Notch up to Long Valley is usually serious ice. Also the mile before Grubb's Notch is often treacherous. We're talking real crampons, ice axe, and the requisite skill to use them. By the time you hit all of this you will have traveled about 8 miles and gained 7,000 in elevation.
So, not advisable unless one has serious mountaineering skills and the equipment to go with it.
I hope you realize that Cactus to Clouds is 17.5 miles and over 10,000 feet elevation gain. Plus if you think you are going to do it in a day, you have return 5.5 miles back to the tram.
We have had quite a bit of snow the past couple of weeks and it may continue.
I did this in March a few years ago during a low snow year. By the time you get past 7,000 feet you basically have passed the point of no return, unless you started out with a couple of gallons of water or can melt snow/ice. Before I got to Grubb's Notch I was in a serious situation, the ice was that bad. There was no snow or ice until around 7,000 feet because that portion of the mountain gets a lot of sun. The rest is heavily wooded and gets little sun in winter. As soon as I got to the shaded area, there was several feet of snow and it was mostly ice. At this point I knew I was probably beyond my skill level -- there wasn't much choice or options. I was solo, did make it safely to the tram, but it was the scariest situation I have ever been in. I will admit, I was beyond my skill level. I had crampons and an ice axe with me and had to use them.
You may want to consider just taking the tram up and going to the Peak and back to the tram, 11 miles round trip. Don't underestimate this mountain because it is in southern California.
Here are a couple "fair weather" trip reports that might provide you with some information: San Jacinto Loop
Weather: PS Tram Weather
There used to be a lot of good recent information here. I haven't checked it out in several years.
San Jacinto Forum
edited to fix url links.