1st a before and after graft done with cling wrap. Note, I don't like this method, but it does work. What you are looking at here are two seedlings grafted together inside this little wedge. I like to share this one as it shows a little light through the bottom and one side indicating that the connections are not perfect. They don't have to be, but imperfections like this can occur due to removing the cling wrap too soon and allowing the tissue to dry out on the side.
They can also simply occur due to improper alignment/
jagged cuts from multiple slices--try to make just one cut or two in the case of a wedge graft when possible.
jarring during or after grafting via bumping -- happens most often when the graft is not secure enough
pulling at the graft/happens when one removes cling wrap. Often caused by spines hanging up in the cling wrap or being too hasty with the removal.
Now, to your question... how long to leave the cling wrap on. That depends on how fast your stock is growing, but as a general rule 1-2 weeks is adequate time to leave cling wrap on. However, like parafilm... if you simply allow nature to do some of the work of removal for you then you will often fare better. Leaving cling wrap on too long can stunt or deform a graft. Keep an eye out as your stock may grow faster or slower. Another reason when I graft with this method I look at my grafts daily.
This is what I mean. With parafilm I can leave the wrap on indefinitely. The scion simply grows through the parafilm and the parafilm eventually falls off. No worries.
With cling wrap, I simply remove the holding device... in this case a clothespin and allow the cling wrap to loosen up on its own over several hours. When I come back if it is not sufficiently loose I can pull at the edges bit by bit to loosen it up. Problems mainly occur if spines are left on catch in the cling wrap. Removal of spines helps with cling wrap in my opinion to prevent those spines from catching and pulling at the cling wrap. However, even leaving them in they are rarely a problem unless they are sufficiently stout and long and the graft has barely taken. Bottom line, if you have have any worries... leave it be is often after you have unsecured your parafilm. As your graft grows stronger and bigger it will generally finish popping off the parafilm for you. Never rush a graft is my motto, but we are all guilty of it from time to time. I know when I first started grafting some few decades ago I ruined a great many grafts by rushing to peak or looking too soon. I still do as a matter of fact as now I have the added experience and knowledge on how to mess up my grafts with style. Impatience is never good.
Seedling graft on Trichocereus. I also did with cling wrap. That one was only left in place for a single week if memory serves. I had to remove the cling wrap as black mold started to creep in... another draw back I have found that occurs for me more often when using cling wrap rather than parafilm. My personal remedy to the black mold if I catch it early is to poke holes in my cling wrap to let it breath just a little.
Lastly, one need not use any wrap at all as was the case with this triple graft. Notice the bottle remains around it. I like this style as its fun and makes use of water bottles, gatorade, powerade, etc. type bottles. Simply cut and fill with dirt and your stock plant leaving the top attached on one side to the bottom of the bottle. I.e. don't cut the bottle all the way through. Now, with this style graft you rely on a slight humidity provided by the micro green house you will create when you fold the top of your bottle back over your grafted scions. Wrap the finish product with tape and secure in a position where it gets dappled sun light and no more 1 hour of direct sunlight in a day. If too much water condenses in the bottle... remove the cap and let it vent. If there is not clear humidity and condensation in the bottle you can use a straw to put a little water down the sides of the bottle. Not too much though and make sure not to water this bottle or the stock Pereskiopsis for 3-5 days prior to grafting or your grafted seedlings that are unsecured will likely simply float off. You can also cheat with this method and simply use parafilm. to secure your seedlings to the graft. After 7-14 days depending on rate of growth... I will then water. Remove cap for a few days. Then remove top of bottle if no signs of scion drying out are present. If scion appears to be drying out... mist or add water and then cover again.
Hope that helps you my friend.
Next time.... parafilm! Laughing... so long as your method works 97.5% of the time for you or more... I don't think it really matters which technique you become proficient at. Lets get everyone to that 97.5% success rate or better mark though. That last statement is my greed talking as I love seeing new eye candy fast!