I hear from time to time that some people are not organised or can remember to share photos on their Instagram account. So I am here to write out basic services you can use to help schedule your photos onto Instagram. I won’t explain how to set up these services as they have instructions within the app.
Photogrid
Before we start talking about scheduling apps, you’ll need a photo editing app which can wither crop photos or add borders into an Instagram Square photo. Any photo shape that is not square format, you’ll have the scheduling app to manually add the photo onto Instagram and won’t share automatically.

Note: Please consult with the photographer that it is OK to crop and add borders to their photos. From my point of view, should a cosplayer ask me if this is OK to modify my photos, I would be fine with it, though can’t hurt to ask. Reminder, not to add on top and filter or further edit a photographers work.
Buffer
This service can be both found as an app and also as a website at www.buffer.com. When setting up, you’ll be asked to change your account type to a business account, do not panic, this just opens up more features and it’s free of charge and does not fundamentally change the look or the usage of your account.
This service you can schedule post not just on Instagram, but also twitter, Facebook, pintrest, and linkedin.
Their service has a premium and free plan where the free plan you can schedule up to 10 photos per social account and can run up to three social media accounts. The free plan allows you to continuously schedule up to 10 photos, so you can keep topping up each social media account and spread them out as often or as little as you like. I tend to top up most evenings when I am at my laptop but also I can add on the fly, from my mobile phone, upload Instagram friendly photos.
When scheduling posts you can either individually share photos to each separate social account, or highlight all or some of the social accounts, and schedule that one photo over multiple accounts without re-typing up the body of the post.

Later.com
Later.com is very similar to Buffer in terms of service and feature, but the main real differences that you can only share up to 30 photos per month per social media account. Each month, your allowance to upload photos resets at the beginning of the month.
All the features mentioned in buffer such as sharing over different social mediums such as twitter, facebook as well as Instagram is there. Also can select multiple accounts to share a single photo.
Later.com allows you upload all the photos to there server, ready to share photos over time, so you do not need to wait to upload your photos, you can upload all your photos you want to share, and Later.com will keep track of which photos have been used so you don’t duplicate what works has already been shared.

Other Services…
I would like to mention that Facebook within their Creator Studio app, where you can share the Instagram post but I have to say that I have not used their service so can’t comment on how the workflow is.
But, recently I have found using Facebook Pages/Creator Studio not very intuitive on how to use their service, compared to how Buffer and Later.com allow you to upload and schedule posts.
I use both these services for both my photography brand of Food And Cosplay and AitchKayCee, and each have there benefits. It would be up to you which of the two fits your workload/lifestyle and how much time you want to spend on scheduling photos onto Instagram/social media.