Your trip depends, on of course the strength of the blotters.
The setting, music, your mood (whether you angry or happy) also affects the trip.
Take one, see how you feel within 30minutes, if you don't feel much difference take another and relax for a while.
What works best for me, is that i take two blotters, after half an hour i got for a cigarette in cold air and it hits me straight away, and the nicotine rush helps boost it.
Have a good trip and take care.
First, if you don't feel like anything in 30 minutes you don't need to re-dose yet. Around 45-50 minutes, or 60 minutes if you've eaten, you should start getting worried.
Also, as far as I know the time LSD is actually active in the brain is a very short time, so redosing is often ineffective other than for purposes of "restarting" and extending the trip; ie. the doses don't cumulate as such. What I've read on it and how I've experienced it in practice seems to support this, but I dunno what you guys reckon. So 100ug taken at once is much more potent than 50ug + 50ug taken, say, 60 minutes later.
The drug has set its effect into motion, but is no longer active, and another dose will not increase the amount of acid acting in the brain all that much. It's got a very short half-life as well.
If at all possible, take your dose, and if after 45-50 minutes you don't feel a thing at all, take 1.5 or 2 times that dose, provided you have access to more acid. I have known of people taking one blotter, then taking another an hour later and just barely tripping, and having highly unpleasant not-quite-there experiences. I have also taken a starter of 2 hits, and then went on to take approximately 10 more, give or take (1 or 2 at a time), throughout the day and never been tripping harder than the first hour or two of the first two hits. Tolerance also obviously causes this.
So try to dose a decent amount, wait a good while, and if you feel the need to wait, re-dose with a slightly higher amount if possible.