How long is too long to express colostrum at one time?

[mumtobeoct22]

I started expressing colostrum at 36 weeks as advised by my midwife as I have GDM. I have found it quite easy and have expressed far more than I thought I would so far. I hadn’t realised yesterday that 30 minutes had gone by as I was expressing so much but when I was doing some research today I found that you’re only supposed to express for 3-5 minutes at a time. Is there a reason for this, am I going to do any harm to express for longer periods than this?

If you feel any contractions stop, otherwise you're okay. I have to express for that long several times a day as it takes so long, but I have insurmountable supply problems so colostrum is really the only thing I can provide for my baby.